Since now all articles have a class, the `Usage:` is unnecessary. This
PR will remove them.
(cherry picked from commit e7757aa4be3ecb067749df226043e61a12b62d82)
* prevent pull request to be merged when PR is a WIP
* add tests
* add helper to prepend WIP: in PR title
* move default wip prefixes into settings
* use configurable WIP prefixes in javascript and default to first one in templates
* add documentation
* add unit test on pull model
Signed-off-by: Julien Tant <julien@craftyx.fr>
