Sanitize `data` and `vbscript` links

Closes #13625 

Closes https://dev.gitlab.org/gitlab/gitlabhq/issues/2660

See merge request !2905

Branded appearance to CE

Closes #11489 

The difference with the EE version is only that there is no distinction between light and dark logos, though this wasn't used anyway. If this is fine, I'll create a MR on EE too.

TODO:
- [x] Copy docs
- [x] Make new screenshots
- [ ] Remove Custom Welcome message feature?

@rymai: I was unsure what labels to add to ping you, so I just ping you like this 😉 

/cc @DouweM

See merge request !2927

Don't repeat labels listed on Labels tab.

Fixes #13622 

See merge request !2924

Improve discoverability for CI examples

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/13410

See merge request !3008

[ci skip]

Add "Gotchas" to development docs

Also:

- Alphabetizes the "Developer" index page
- Fixes the broken `db_dump.md` link

See merge request !2846

[ci skip]

Adjust documentation of permissions

## What does this MR do?
This MR improves the documentation of the permissions by mentioning that internal projects do not enforce the Guest role.
## Are there points in the code the reviewer needs to double check?
No code was touched - only the documentation was adjusted.
## Why was this MR needed?
Without this adjustment it might not be clear how you can set up an internal project to be pullable by everyone whilst having the issue tracker and labels managed by permitted people only.
## What are the relevant issue numbers?
#13679 

See merge request !2925

[ci skip]

Fix issue milestone filter spec

See merge request !2990

Strip leading and trailing spaces in URL validator

_Originally opened at !2914 by @evuez._

It makes URLs in webhooks valid even if they contain leading and/or trailing spaces.

Spaces are hard to notice in input fields, this helps users by accepting leading and trailing spaces in webhooks URLs.

Fixes #13652

See merge request !2939

Refactor Repository Caching

Related issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/13515

See merge request !2936

Fix avatar stretching by providing a cropping feature

Originally by @nesk at https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2773

Fixes #7959

See merge request !2951

Created helper class to hide content in issue sidebar when collapsed

![Screen_Shot_2016-02-25_at_10.38.39](/uploads/ca49cc230edf7e71b7726e905f523092/Screen_Shot_2016-02-25_at_10.38.39.png)

Closes #13764

See merge request !2968

Add builds URL to gitlab-ci script

Add builds URL to gitlab-ci script

Related to: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2681

See merge request !2962

Refactor html/css for lists and improve help UI page

* dry lists html/css removing a lot of style duplicates
* fix snippets list to match common style
* fix extra bottom margin for groups list
* improve help page ui so it looks clean

Fixes #11873 

See merge request !2977

The only major difference with the EE version is the change from a light and dark logo to only a header logo
The dark logo wasn't used anyway, so it seemed to make sense to me to rename the field to the actual function of it

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fix syntax error in autosave coffeescript.

According to http://coffeescript.org/#try , `catch` needs to have an argument.

Otherwise, `Error: Parse error on line 19: Unexpected 'INDENT'` error is raised when converting to JS by coffee-script.

Fixes gitlab-org/gitlab-ce#3302


See merge request !2985

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>