This MR simplifies CI permission model:
- read_build: allows to read a list of builds, artifacts and trace
- update_build: allows to cancel and retry builds
- create_build: allows to create builds from gitlab-ci.yml (not yet implemented)
- admin_build: allows to manage triggers, runners and variables
- read_commit_status: allows to read a list of commit statuses (including the overall of builds)
- create_commit_status: allows to create a new commit status using API

Remove all extra methods to manage permission.
Made all controllers to use explicitly the new permissions.

This should help us detect potential regressions in the future.