Fix conflicting keyboard shortcuts and update overlay

This fixes search/star and archive/select all conflicting, cleans up
mark read/unread conform to the HIG, and updates the help overlay and
fix some problems with it.
4 jobs for wip/shortcut-conflicts in 21 minutes and 6 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #396072
ubuntu

00:09:49

 
  Test
passed #396073
flatpak

00:10:09

 
  Deploy
passed #396074
review

00:00:35

passed #396075
allowed to fail manual
stop_review

00:00:31