Use the relative url prefix for links in Wiki

Retry of gitlab-org/gitlab-ce!4026

@rymai !4050 solved all other problems how it looks like. I [tested](https://gitlab.com/artem-forks/gitlab-ce/commit/ff01eca7b559efa7cacf3412aa01cd8ae8a6db7e/builds) this with ruby22

Fixes #17071 



See merge request !4131

Create import data in service and fix timing issues when scheduling job

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/17401

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/17376

See merge request !4106

Fix an issue when filtering merge requests with more than one label

Fixes #15529.

See merge request !3886

Fix build notification on merge request page change even if the build status didn't change

## What does this MR do?
This MR contains a bugfix for #17357 which was introduced by !3998. The notification are now only shown on status changes, and not when switching between different merge requests.

## Are there points in the code the reviewer needs to double check?
Check implementation

## Why was this MR needed?
Because auf a bug introduced in !3998.

## What are the relevant issue numbers?
#17357

Closes #17357

See merge request !4086

Relative Links in the Wiki Are Broken

- [ ] #16568 (!4050) Relative links in wiki are broken
    - [x] Investigate issue

  
    - [x] Implementation / Fix

        - [x] Write (failing) tests for `WikiLinkFilter`
        - [x] Link to `./bar` should either get rewritten correctly or left alone
        - [x] Link to `./bar.md` should maybe get rewritten correctly (is left alone currently)
        - [x] Link to `bar.md` should get rewritten correctly


            - [x] Check if this indeed a bug

    - [x] Make sure CI is green
    - [x] Assign to endboss

    - [x] Wait for review

    - [x] Implement review feedback
    - [ ] Wait for merge


See merge request !4050

This MR never made it into 8.7.4.

[ci skip]

This reverts commit d1ba0986.

[ci skip]

Use a case-insensitive check to compare URI schemes

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/17299

See merge request !1965

Add if exists to drop command

Add `IF EXISTS` as a precaution. Related to gitlab-org/gitlab-ce!4020

See merge request !4100

Rake drop tables with cascade

See merge request !4020

Fix build notification on merge request page change even if the build status didn't change

## What does this MR do?
This MR contains a bugfix for #17357 which was introduced by !3998. The notification are now only shown on status changes, and not when switching between different merge requests.

## Are there points in the code the reviewer needs to double check?
Check implementation

## Why was this MR needed?
Because auf a bug introduced in !3998.

## What are the relevant issue numbers?
#17357

Closes #17357

See merge request !4086

Allow Redmine issue references to work as intended

Closes #14527 and #14894 

See merge request !4048

Use sign out path only if not empty

Fixes: https://github.com/gitlabhq/gitlabhq/issues/10066

See merge request !3989

Pass trusted_proxies to action_dispatch as IPAddrs instead of strings

Without this setting your own trusted_proxies does not work.

Fixes an issue introduce in: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3524

Fixes: https://gitlab.com/gitlab-org/gitlab-ce/issues/17004

See merge request !3970

Fix importer bug when throwing exceptions

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/15681

See merge request !3941

Initialize wikis on legacy projects during check

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/4173

Helps https://gitlab.com/gitlab-org/gitlab-ce/issues/15423

See merge request !3931

Fix the line code when importing PR review comments from GitHub

Pull Request Review Comments are comments on a portion of the unified diff.

Closes #17205

See merge request !4010

Merge request widget displays TeamCity build state and code coverage correctly again

## What does this MR do?
This MR contains a fix for a regression introduced in `8.7`. In former version, the TeamCity build status was always displayed correctly. In `8.7` the build state is still checked, but the UI is not updated correctly any longer.

## Are there points in the code the reviewer needs to double check?
The changes are quite simple, so please simply double check them.

## Why was this MR needed?
This MR is needed to make the TeamCity build status working again.

## What are the relevant issue numbers?
#17080 

See merge request !3998

Instrument methods used in email diffs

See merge request !4038

Updated spacing between notification label and button

![Screen_Shot_2016-04-28_at_11.36.26](/uploads/7b33e78e85688d96f878272ee93038ba/Screen_Shot_2016-04-28_at_11.36.26.png)

Closes #16552

See merge request !3965

Fix error when trying to create a wiki page

Closes #15527, #15569, #15623, #15630, #15637, #15653, #15870, #16558, #16875, #16987, #17016, https://github.com/gitlabhq/gitlabhq/issues/10317.

See merge request !3924

Load the "New Branch" button asynchronously

Here's how it looks like for logged in users:

![new_branch](/uploads/718e3d9016a50a0432b9541dde5ca74c/new_branch.gif)

And here it is for anonymous users (or when a new branch can't be created by a logged in user):

![new_branch_anonymous](/uploads/dce42ee6a7dd7708443cdfdb56389d46/new_branch_anonymous.gif)

See merge request !3855

Updated label links to work correctly for filtering

See !3846#note_5033951

See merge request !3920