Update merge_requests.md.

Error in 'Approve merge request'  section in API documentation

## What does this MR do?

Just fix an error in API Documentation in 'Approve Merge Request' section. 

Url in documentation : 
`POST /projects/:id/merge_requests/:merge_request_id/approvals`

Should be : 
`POST /projects/:id/merge_requests/:merge_request_id/approve`

(Verified on gitlab 8.12.7-ee 4051516)

See merge request !809

Cache the last usage data to avoid unicorn timeouts

On GitLab.com, the usage data cache was never populated because it takes longer than 60 seconds to generate.

This MR also improves usage data performance. The Event default_scope was causing the query to use the wrong index, causing the query to scan through all rows unnecessarily.

Closes #1044

See merge request !779

Use Ruby 2.1-compatible hash syntax for boards

This broke the master build, because we only run Ruby 2.1 specs on master. https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6978 wouldn't help because this is in Haml 😞

See merge request !808

Add a wait_for_ajax call to prevent Spinach failure

There may be a race condition after a user clicks "Rebase" and when
the DatabaseCleaner wipes all data.

See https://gitlab.com/gitlab-org/gitlab-ee/builds/5302296

See merge request !810

Show a flash message in the project's main view when it's repo is
over the limit.

Fixes #1042 

See merge request !762

There may be a race condition after a user clicks "Rebase" and when
the DatabaseCleaner wipes all data.

See https://gitlab.com/gitlab-org/gitlab-ee/builds/5302296

The Event default_scope was causing the query to use the wrong index,
causing the query to scan through all rows unnecessarily.

Closes #1044

Restrict pushes / merges to a protected branch to specific groups

- Closes #675 and https://gitlab.com/gitlab-org/gitlab-ce/issues/21153
- Related to #179 

**Default State**
![Screen_Shot_2016-09-22_at_12.53.27_PM](/uploads/3777bc09fc5b0f9ddeccbf52dbf0277e/Screen_Shot_2016-09-22_at_12.53.27_PM.png)

**Filtering**
![Screen_Shot_2016-09-22_at_12.53.39_PM](/uploads/1e649e2a3720a4b0d7ff3e4fbafe5a72/Screen_Shot_2016-09-22_at_12.53.39_PM.png)

# Tasks

- [ ]  ee#675 !645 Restrict pushes/merges to specific groups
    - [x]  Implementation
        - [x]  Basic model-level implementation
        - [x]  Test / refactor
        - [x]  Rudimentary frontend (controller actions + autocomplete for the dropdown)
            - [x]  Groups that a project hasn't been shared with can't be selected
        - [x]  Look for edge cases
    - [x]  Questions
        - [x]  What are LDAP group links?
            - A GitLab group can be synced with one or more LDAP groups
            - The sync happens in an async task, an the LDAP group users are _imported_ into the GitLab group
            - `group.users` on a GitLab group returns the LDAP group users as well (after the import task has run)
            - We check `group.users` for this feature, so we shouldn't need any additional work to support LDAP groups
    - [x]  CHANGELOG
    - [x]  Removing a group should remove the access
    - [x]  `autocomplete/groups` issue
    - [x]  Fix uniqueness validation
    - [x]  Assign to @alfredo1 for UI work
    - [x]  Wait for !581 to be merged
    - [x]  Rebase against EE master instead of !581
    - [x]  Add feature specs
    - [x]  Implement frontend
    - [ ]  Assign to endboss
    - [ ]  Get backend + frontend reviewed
    - [ ]  Wait for merge


See merge request !645

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

Error in approve merge request api url in API documentation

Add ability to have multiple issue boards for a single project.

https://gitlab.com/gitlab-org/gitlab-ee/issues/929

https://gitlab.com/gitlab-org/gitlab-ee/issues/1084

See merge request !782

Updated generate URL

Redirects back to issue boards index after deleting