Updated the milestones API documentation and added return codes descriptions.

The notes API documentation updated with return codes. API now returns `400 Bad Request` if
required attributes are not present. Return codes are documented now, also tested in added tests.
The documentation now reflects the current state of the API.

Conflicts:
	spec/requests/api/projects_spec.rb

Fix RESTfulness of project hook deletions by API

Fixes a test that checks if the project limit is reached.

Conflicts:
	spec/requests/api/projects_spec.rb

The users API updated with return codes, e.g. if required parameters are missing
a `400 Bad Request` error is returned instead of `404`. Fixes return codes of functions,
e.g. deletion of a ssh key is an idempotent function now.
The API documentation is updated to reflect the current status of the API. Descriptions
are more detailed and complete, infos to return values are added to all functions.

API: creating last project before limit returns 404

API: fixes visibility of project hook

Add commit full time tooltip to `commited_ago`

Update doc/install/installation.md

Update seeds for state columns

changed installation overview list step #4
Gitolite -> GitLab shell 

Event already has author relation

Fix development fixture for gitlab_shell

Conflicts:
	app/models/issue.rb
	app/models/merge_request.rb

Sort groups alphabetically on dashboard page

Minor changes to installation and databases docs.

Change .gitignore to ignore logrotated log files.

Add option to disable username changing

Ssh fingerprint fix