timeline: Regroup actions setup logic
timeline: Move text constants in the method where they are used
viewer: Focus back the timeline when using the buttons

This means the button will lose focus when it's activated. The goal is
for the timeline actions to remain enabled, as they are disabled when
the timeline or ruler loses focus.
timeline: Disable the selection actions when timeline focused but there is no selection
dogtail: Fix some
viewer: Darker viewer at the start
application: Simplify the code by removing a method
application: Remove unused code from application
application: Remove unused signals
mainwindow: Allow Ctrl-Q to close the app