Restrict users API endpoints to use integer IDs

Closes #2267

See merge request !1156

Fix HTML link that was improperly escaped in new user e-mail

### Before:

![image](https://gitlab.com/stanhu/gitlab-ce/uploads/e42e73f04971d8dd949b034846d2bb9f/image.png)

### After:

![image](https://gitlab.com/stanhu/gitlab-ce/uploads/90425911345031a4b8e9374323728f79/image.png)

Closes https://github.com/gitlabhq/gitlabhq/issues/9640

See merge request !1323

Closes https://github.com/gitlabhq/gitlabhq/issues/9640

See merge request !1306

Add missing proxy requests to migration docs

See merge request !1317

Change 7-14-stable to 8-0-stable in doc/install/installation.md

Also fixes sudo user from previous MR.

[ci skip]

See merge request !1320

[ci skip]

[ci skip]

Fix 7.14 to 8.0 update guide

[ci skip]

See merge request !1319

Fix confusing behaviour of back link in CI sidebar

Back link should always be responsible for sidebar navigation below.
It should change sidebar navigation to one level up

See merge request !1316

Style CI projects page and builds list

Partly implements #2545

See merge request !1315

Fix default avatars to ensure that helpers don't have /assets dir appended

See issue #2555

See merge request !1314

Allow configuration of LDAP attributes GitLab will use for the new user account.

Fixes #2412.

See merge request !1261

Back link should always be responsible for sidebar navigation below.
It should change sidebar navigation to one level up

Add links from GitLab to CI

* link from dashboard to CI dashboard
* link from project to CI project

Its a fast solution for 8.0. Might be improved in later versions
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !1313

Fix first bunch of regressions in GitLab CI

/cc @vsizov @dzaporozhets

See merge request !1312

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

Fix in Markdown help page: properly create the link to a wiki page.

The help file on Markdown that is included with Gitlab CE (7.14.3 d321305c)
and also gitlab.com (see https://gitlab.com/help/markdown/markdown#links)
contains a typo in the description of a link to a wiki page.

See merge request !1310

The help file on Markdown that is included with Gitlab CE (7.14.3 d321305c)
and also gitlab.com (see https://gitlab.com/help/markdown/markdown#links)
contains a typo in the description of a link to a wiki page.

Merge CI into CE

First step of #2164.

- [x] Merge latest CE master
- [x] Make application start
- [x] Re-use gitlab sessions (remove CI oauth part)
- [x] Get rid of gitlab_ci.yml config
- [x] Make tests start
- [x] Make most CI features works
- [x] Make tests green
- [x] Write migration documentation
- [x] Add CI builds to CE backup

See merge request !1204