Geo documentations improvement for 8.9

Important changes:

* Added note that we don't support MySQL (I don't know if we should add to the limitations or not)
* Added related files to the TOC
* Added disaster recovery instructions (we don't support this, but there are manual steps if anyone need)
* Added troubleshooting instructions

From recent feedback:

We need to improve the SSH keys part of setup instructions, as it's unclear which ssh key you have to add at geo nodes screen and that you have to pre-authorize the connection once (add to known_hosts), so clones can actually work.

Fixes gitlab-org/gitlab-ee#344

See merge request !431

Don't reset approvals after rebase from UI

Rebasing from the UI should be considered a 'safe' action, so this
should ignore the 'reset approvals on push' project
setting.

Unfortunately, as rebase is implemented by working directly on
a copy of the repository and pushing (as it's not supported fully by
libgit2), we can't detect this purely with information available to the
PostReceive job. If we used commit metadata, the MR author could also
add the same metadata and push without resetting approvals.

To work around this, add a new column to the MergeRequest model to store
the SHA from the rebase action. (Ensure that this is set before pushing,
to avoid a race condition!) Then, in PostReceive, don't reset approvals
if the pushed SHA matches the SHA stored in the database.

![Approval_reset](/uploads/cc3ae5f417d403b271aa25884af8f54b/Approval_reset.gif)

Closes #372.

@DouweM this was marked as 8.9 but I think it's a bit close to be adding ~"Pick into Stable" - what's the procedure for this? I'm open to changing this implementation; @vsizov and I discussed it this morning and this was the simplest solution we came up with.

See merge request !489

Fix link to permissions



See merge request !495

Rebasing from the UI should be considered a 'safe' action, so this
should ignore the 'reset approvals on push' project
setting.

Unfortunately, as rebase is implemented by working directly on
a copy of the repository and pushing (as it's not supported fully by
libgit2), we can't detect this purely with information available to the
PostReceive job. If we used commit metadata, the MR author could also
add the same metadata and push without resetting approvals.

To work around this, add a new column to the MergeRequest model to store
the SHA from the rebase action. (Ensure that this is set before pushing,
to avoid a race condition!) Then, in PostReceive, don't reset approvals
if the pushed SHA matches the SHA stored in the database.

Users with master permissions cannot edit the file locks

Fixes https://gitlab.com/gitlab-org/gitlab-ee/issues/702

See merge request !494

Set no container on locked files sub nav

Closes #703 

![Screen_Shot_2016-06-21_at_12.44.27_PM](/uploads/5e95a838256650d07260ea2639e3a302/Screen_Shot_2016-06-21_at_12.44.27_PM.png)

cc @dzaporozhets 

See merge request !492

Allow setting required approval count on MR

Closes #314.

See merge request !470

Address review comments for !440

See merge request !486

Send notification email when MR is approved

Closes #42.

See merge request !484

Fix Error 500 occuring when sorting merge requests by "More weight" or "Less weight"

This MR moves weight scopes & sort methods to `Issue`.

This ensure `MergeRequest` won't try to sort by weight, which would fail
since it doesn't have weight.

It also show the "sort by weight" links only when in the context of issues.

See merge request !483

Subnav when viewing the locked files is not highlighted

Fixes https://gitlab.com/gitlab-org/gitlab-ee/issues/700

See merge request !488

Change projects to project

Fixes wrong path in doc structure

See merge request !490

[ci skip]

Fix git hooks when commit goes from web UI

Fixes https://gitlab.com/gitlab-org/gitlab-ee/issues/587

See merge request !487

Documentation for File Lock feature



See merge request !485

- Move to new location according to
  https://gitlab.com/gitlab-org/gitlab-ce/issues/3349
- Use new images

Remove explicit Gitlab::Metrics.action assignments, are already automatic.

See merge request !473

Add LDAP EE docs

Add specific documentation for LDAP in EE. I chose to create a new file to reduce the chance of overwrites when CE gets merged to EE. 


See merge request !367

Signed-off-by: Rémy Coutable <remy@rymai.me>

This ensure MergeRequest won't try to sort by weight, which would fail
since it doesn't have weight.
Signed-off-by: Rémy Coutable <remy@rymai.me>

UpdateMirror service return an error status when no mirror

See merge request !482

Fix Error 500 when attempting to sort merge requests by weight

Fixes #673

See merge request !477

Fixes #673

Fix JenkinsService test button

When clicking the "Test" button on the JenkinsCI Service, the following error occurs:

```
We tried to send a request to the provided URL but an error occurred: undefined method `message' for [200, ""]:Array 
```

!374 changed the implementation to call the `WebHook`, which returns [status, message], instead of the return value of `HTTParty#post`.

Closes #637

See merge request !476

File Lock

Fixes https://gitlab.com/gitlab-org/gitlab-ee/issues/497

- [x] Data layer(tables, models, migrations)
- [x] Checks on git push
- [x] Author should be able to push if one owns the lock
- [x] Path matcher with tokenizer and memoization
- [x] Show lock status icons by files and folders
- [x] UI: mockup buttons for locking files, folders
- [x] UI: Locking files
- [x] UI: Locking folders
- [x] Permissions check everywhere
- [x] Add page to list all locked files/dirs to get overview in case people forget to unlock
- [x] Refactor `lock_file_button` and `lock_file_link`
- [x] Testing Git LFS
- [x] Get rid of code duplication in pre-receive hook
- [x] Test case: I want to unlock file if I'm a developer and I'm not an author of lock
- [x] Make it EE option
- [x] Specs and spinach
- [x] TODOs in the code

Can be moved to the next iteration:
- [ ] Duplicate lock checks in the service since pre-receive hook does not work for UI (according to Douwe)
- [ ] timeago in the lock icon tooltip. It's not working out of the box.
- [ ] Ajax load bar on click "Lock/Unlock" in the file tree
- [ ] Nested locking UI. If we look at file and it's locked because of parent we should show it in tooltip. 


**Screenshots**

![joxi_screenshot_1466188707474](/uploads/623e65c9a246b07c9786fd8babdb2dd8/joxi_screenshot_1466188707474.png)![joxi_screenshot_1466188735083](/uploads/4588eff352ee544de5bb5727d501a2cc/joxi_screenshot_1466188735083.png)![joxi_screenshot_1466188758950](/uploads/dee7b342c7825a79ed1629535eced5ed/joxi_screenshot_1466188758950.png)


Related info:
Douwe wrote:
```For a next iteration, we need to think about nested locking more. If user A has locked lib/, user B shouldn't be able to lock lib/foo.rb since that falls under lib/. Similarly, if user A has locked lib/foo.rb, user B shouldn't be able to lock lib/, because part of that directory is locked by someone else already.```

See merge request !440

Closes #637