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
This commit replaces the former floating_window_layouter with a new
window_layouter component that supports the subdivision of screen space
into columns and rows, the concept of layers, and the principle ability
to store window layout information across reboots. The latter is
accomplished by reflecting the component's internal state as a 'rules'
report to the outside.
Fixes#3031
