This commit adds dynamic switching in between different defined
screens via keyboard shortcuts, or by editing the rules file.
In the window_layouter package it defines per default ten screens,
reachable by pressing the screen key along with numbers 0-9.
Fix#3646
This commit moves the window layouter and window decorator into
dedicated packages that can now be combined with the "wm" server at
runtime and restarted/reconfigured/swapped-out independently.
To use the window manager, one must start the 'wm', 'window_layouter',
and one of the 'motif_decorator' or 'themed_decorator' subsystems.
Fixes#3024
