V4.0 API fixes

Conflicts:
	vendor/assets/javascripts/branch-graph.js

Fix and refactoring gfm_autocomplete

Rename tasks

Rename add_users_to_project_teams to gitlab:import:all_users_to_all_projects

Rename gitlab:app:db_* to gitlab:backup:db:*
Rename gitlab:app:repo_* to gitlab:backup:repo:*
Rename *_dump to *_create

Update Contribution Guide

Reorganize settings

All overrides are marked as deprecated.
Default settings are at the bottom.

fix dark code preview background when displaying long lines

Added compare switch