LDAP Sync blocked user edgecases

Allow GitLab admins to block otherwise valid GitLab LDAP users
(https://gitlab.com/gitlab-org/gitlab-ce/issues/3462)

Based on the discussion on the original issue, we are going to differentiate "normal" block operations to the ldap automatic ones in order to make some decisions when its one or the other.

Expected behavior:

- [x] "ldap_blocked" users respond to both `blocked?` and `ldap_blocked?`
- [x] "ldap_blocked" users can't be unblocked by the Admin UI
- [x] "ldap_blocked" users can't be unblocked by the API
- [x] Block operations that are originated from LDAP synchronization will flag user as "ldap_blocked"
- [x] Only "ldap_blocked" users will be automatically unblocked by LDAP synchronization
- [x] When LDAP identity is removed, we should convert `ldap_blocked` into `blocked`
 
Mockup for the Admin UI with both "ldap_blocked" and normal "blocked" users:
![image](/uploads/4f56fc17b73cb2c9e2a154a22e7ad291/image.png)

There will be another MR for the EE version.

See merge request !2242

Fix the undefinded variable error in Project's safe_import_url method

Fixes #7982

See merge request !2419

Show referenced MRs & Issues only when the current viewer can access them

This addresses both issues identified in #6066.

## The private MR by user `remy2` with a note referencing to a public issue

![Screen_Shot_2016-01-12_at_16.45.02](/uploads/c245ec2c1fdea1f9ba05183c24e142d9/Screen_Shot_2016-01-12_at_16.45.02.png)

---

## The public issue viewed by user `remy` **who doesn't have access to `remy2/private-project`** before the fix

![Screen_Shot_2016-01-12_at_18.14.50](/uploads/8db5580e803f5bddd6cb935233c579a0/Screen_Shot_2016-01-12_at_18.14.50.png)

---

## The public issue viewed by user `remy` **who doesn't have access to `remy2/private-project`** with the fix

![Screen_Shot_2016-01-13_at_12.02.32](/uploads/cb199f7b78191fba486a11412412e307/Screen_Shot_2016-01-13_at_12.02.32.png)

---

## The public issue viewed by user `remy2` with the fix (no change)

![Screen_Shot_2016-01-13_at_11.54.06](/uploads/ddece590d69f597a95559beddcd36660/Screen_Shot_2016-01-13_at_11.54.06.png)


See merge request !2405

Allow broadcast messages to be edited

Closes #3046 

See merge request !2268

Update button style on milestone pages

See merge request !2414

Update documentation to Go 1.5.3

Security fix: https://groups.google.com/forum/#!topic/golang-dev/MEATuOi_ei4

See merge request !2418

Fix has been introduced in !2224.

Move doc_styleguide in the development directory

Reference #3841 

And also add many new styleguides:

- Naming
- Images
- Links
- Headings
- Formatting
- Notes
- API

See merge request !2386

Added hint that you can search users by name, username, or email.

Fixes gitlab-org/gitlab-ee#19

/cc @JobV 

See merge request !2411

- Fix some syntax/grammar typos
- Link to GFM documentation on newlines
- Be less strict on the alphabetical order styleguide
- You can override the "numbers in headings" rule if you discuss it first
- Do not mention CE in notes if the feature is in both CE and EE

[ci skip]

Closes #3046

- Removes redundant "Create a broadcast message" scenario that was
  entirely covered by the "Create a customized broadcast message"
  scenario.
- Adds "Edit an existing broadcast message" scenario
- Adds "Remove an existing broadcast message" scenario

- Adds default values for `color` and `font` attributes
- Adds `active?`, `started?`, `ended?`, and 'status' methods

Now it returns the fully-formatted message so we can be consistent about
how it's shown.

Also make the feature tests less brittle.

Also resets the default example message when the user input is blank.

- Improve specs for private Issue/MR referenced in public Issue
- Add specs for private Issue/MR referenced in public MR

This is moved to a model method rather than an helper method because the
API will need it too.

See merge request !2406

Fix #9963 reference_filter "Encoding::CompatibilityError" bug with some complex URL;

https://github.com/gitlabhq/gitlabhq/pull/9964

@DouweM

See merge request !2383