Add comments and additional docstrings to some functions on events module.
Excluded the migration files from the tests coverage stats
Remove an space
Close all back task of US #80: Generate US from issues
US #80: Generate US from issues: Generate issue comment automaticaly
Bug#226: Now owners has permissions to do restricted actions
Bug#226: Now owners can be visualized on the users list of  a project
Fix bug #223: Errors in the breadcrumb of the US detail page
Refactored the bulk_update_order function of project api
Now users have better permissions management
Fixing some users api tests
Refactor: create a notification service to use it outside of the ViewSet classes
Close bug #230