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

* 8-4-stable: (285 commits)
  Add Changelog entry for build traces data integrity fix
  Update doc_styleguide.md [ci skip]
  Added hint that you can search users by name, username, or email.
  Add changelog
  Version 8.4.0.rc1
  Randomize metrics sample intervals
  Make the metrics sampler interval configurable
  Don't automatically require awesome_print
  Disable colorization if STDOUT is not a tty
  Block the reported user before destroying the record
  changes `$quote-gray` to `$secondary-text`
  makes message plural for multiple MRs and removes from loop. Duh.
  Prepare Installation and Update docs for 8.4 RC1
  Mention channel/key bug in irkerd docs
  Revert "Remove the `:coffee` and `:coffeescript` Haml filters"
  gets merge request discussion working again
  adds back in discussion.haml.html for issues commenting and closing/reopening properly.
  removing last chunk of MR ajax changes, rest will be in another MR
  reverting more MR ajax files, will appear in different commit
  reverting MR ajax changes, which will be in a different MR
  ...

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.