app: Consider "quit" action for quit

Just like we take a remote "new-window" action into account for
opening new windows, we should call an explicit "quit" action
before falling back to closing all the app's windows on quit.

#624
1 job from wip/fmuellner/better-quit in 1 minute and 11 seconds (queued for 1 second)
Status Job ID Name Coverage
  Source Check
passed #205545
js_check

00:01:11