[Elastic] Stabilize database indexer if database is inconsistent

Fixes https://gitlab.com/gitlab-org/gitlab-ee/issues/459

See merge request !328

update gitlab-elastic-search gem

Fixes https://gitlab.com/gitlab-org/gitlab-elasticsearch-git/issues/3

See merge request !330

Instrument Rails cache code

See merge request !3619

Update gitlab-shell to 2.7.2

See merge request !3594

Use meta key to open todo in new tab

Fixes #15078 

See merge request !3623

Remove TODO for not documented stuff

We should not put a `TODO` in a released product.

See merge request !3553

First pass at a Testing styleguide

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/14121

[ci skip]

See merge request !3465

Use more accurate timestamps for InfluxDB.

See merge request !3617

This allows us to track how much time of a transaction is spent in
dealing with cached data.

Use gitlab-workhorse 0.7.2

See merge request !3570

This is the inverse of 51894dbb.

This changes the timestamp of metrics to be more accurate/unique by
using Time#to_f combined with a small random jitter value. This
combination hopefully reduces the amount of collisions, though there's
no way to fully prevent any from occurring.

Fixes gitlab-com/operations#175

API: Expose subscribed? on issues and merge requests

This is the first start for the new `subscribable` API. It exposes the `subscribed` field for issues and merge requests.

Related to #6024

See merge request !3611

Fix Incorrect Quote In Docker Executor Example

## What does this MR do?
The corrected line opened with a regular quote (') but closed with a back-tick (`)  
I believe this is invalid bash syntax

## Are there points in the code the reviewer needs to double check?
Probably not

## Why was this MR needed?
Fixes error when example is copied and pasted

## What are the relevant issue numbers?
None

## Screenshots (if relevant)
None

See merge request !3604

Remove changelog entry for new navigation sidebar.



See merge request !3608

Fix side-by-side code format & commit message wrap

![Screen_Shot_2016-04-07_at_1.31.28_PM](/uploads/bad00284e4dfbec1fdd75220c34f4a98/Screen_Shot_2016-04-07_at_1.31.28_PM.png)

![Screen_Shot_2016-04-07_at_1.32.23_PM](/uploads/7cd344765025e93d0035934a473b4bb3/Screen_Shot_2016-04-07_at_1.32.23_PM.png)

See merge request !3605

Revert "Merge branch 'new-navigation-prototype' into 'master'"

This reverts merge request !3494

See merge request !3607

[ci skip]

[ci skip]

This reverts merge request !3494

Revert "Merge branch 'fix-sidebar-exapnd' into 'master'"

This reverts merge request !3520

See merge request !3606

This reverts merge request !3520