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

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

It consolidates these endpoints:
 - /projects
 - /projects/owned
 - /projects/visible
 - /projects/starred
 - /projects/all

Into the /projects endpoint using query parameters.

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

Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/8987#note_22938402

This way we could reuse this pool for other migrations

Feedback:

* https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/8987#note_22923350
* https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/8987#note_22923365

Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9192#note_23293693

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

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

We don't need to connect when requesting the name of the database
adapter. This in turn should prevent us from requesting/leaking
connections just by asking whether we're using PostgreSQL or MySQL.

This method allows one to create foreign keys without blocking access to
the source table, but only on PostgreSQL.

When creating a regular foreign key the "ALTER TABLE" statement used for
this won't return until all data has been validated. This statement in
turn will acquire a lock on the source table. As a result this lock can
be held for quite a long amount of time, depending on the number of rows
and system load.

By breaking up the foreign key creation process in two steps (creation,
and validation) we can reduce the amount of locking to a minimum.
Locking is still necessary for the "ALTER TABLE" statement that adds the
constraint, but this is a fast process and so will only block access for
a few milliseconds.

This reverts commit b7c5ca49, reversing
changes made to 9745c98b.

Reason for renaming is to comply with naming convention of services in
codebase.

Given the the Issuable class will soon also have to support MRs this
signals that it can only be used by issues.

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

* Changed name of delete_user_service and worker to destroy
* Move and change delete_group_service to Groups::DestroyService
* Rename Notes::DeleteService to Notes::DestroyService

Cherry-picked 'Remove colorize methods that weren't in CE.'

The create and edit actions for projects had these parameters:

- `public` (optional) - if true same as setting `visibility_level = 20`
- `visibility_level` (optional)

Remove the `public` parameter to avoid contradiction.

Cherry-picked ‘Fix syntax error in conditional statement’