Added note about using CI without GitLab

Because of tweet https://twitter.com/davidlorand/status/635192133557874688

cc/ @sytse @Kamil 

See merge request !168

Add unreleased 8.0 entry to CHANGELOG

[ci skip]

See merge request !242

Order commits by committed_at and id

This needs to be done that way, because the committed_at can be null for some pretty old commits.

This is needed to resolve the issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/2339

See merge request !240

Fix skipped svg

See merge request !241

This needs to be done that way, because the committed_at can be null for some pretty old commits.

Implement build trigger API

This commit implements Build Triggers.

There are changes to API request:
- Due to security advised method to pass trigger token is to use form data
- Advised method to pass variables is to use form data

TODO:
- [x] Implement API
- [x] Implement UI
- [x] Dimitriy and Valery review
- [x] Write specs
- [x] Write documentation
- [x] Job documentation review

See merge request !229

Fix navigation icons

See merge request !239

Fix variable saving error

This is regression not allowing to save the variables if the variable name exists in other projects. This also fixes error rendering issue for variables, which previously was rendered on project's settings page.

See merge request !237

Add example for testing clojure application

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

See merge request !238

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

API for trigger when requested returns trigger request with commit information, but without the created builds

Require the variable key to be set and unique

See merge request !234

Add missing stage when doing retry on a build

See merge request !236

Make the YAML validation more stricter

- deny all globals that are not hashes and doesn't contain script, the
  script is required now
- verify that script is either string or array of an strings

See merge request !235

- deny all globals that are not hases and doesn't contain script, the script is required now
- verify that script is either string or array of an strings