images: Remove unused background image

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Improve handling of sections

* Rename database field from 'name' to 'section' (fixes TODO).

* Use first free section for new windows.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
control: Use wmHide, wmShow functions to toggle visibility of a window

wmHide, wmShow use the external program wmctrl instead of xdotool.

There is no reason why we should use more than one method
to show or hide a window.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
control: Update screen layout when switching windows

This fixes a TODO item.

Signed-off-by: Stefan Weil <sw@weilnetz.de>