Add packages for ed, mksh, zsh, fish, lnlauncher.
BootManager: add a permanent "Quit" button.

As suggested on the mailing list by stippi and korli, it is important to
let the users know they can quit at any time, and it's sometimes the
only thing they can do.
MediaPlayer: reintroduce "stop" shortcut.

It turns out there are some people actually using it, mainly when
playing music. If you interrupt music, you often want to start listeing
from the start of the track again (unlike for video), so having a stop
button makes sense in that case.