It's likely that the PR pages are seen more commonly than the
dashboard by most users, so add alerts there in case users wonder
what's happening.
Fixes#580
- code in the various menus added over time through the UI (queues,
configuration, ...)
- update / improve PR layout a tick
- fix "outstanding forward ports" count on the dashboard
- improve hover title / help on dashboard
- add date of last modification (usually date of success / failure)
- make casing more coherent (everything lowercase)
- add explicit note that UTC date on staged at label is staged at datetime
- rediscover yet again that the staging information is when hovering
on the staging *except the staged at label*
- improve `PullRequest.unstage` to always insert the PR at the start of the
reason when cancelling the staging, for clarity / traceability
Closes#560, closes#609
