Have some uri like `/apps/<appname>/latestjob` that points to the latest job completed/ongoing for an app

[yalh76]

When working on update_app_levels PR's, it would be better to have the last job even in the scheduled state.

Because we use to restart failed job to be sure that the level decrease is accurate.
Several minutes later, when clicking to https://ci-apps.yunohost.org/ci/apps/calckey/latestjob, it will show the last done job even if the one we have restarted is still scheduled