Change the way how effects can get mouse events

With the removal of BoxSwitch all effects which want mouse events use the
fullscreen input window. The available functionality is too complex both
in EffectsHandler and in the Effects.

With this change only fullscreen input windows are supported and all
effects share the input window. This means there is at maximum one input
window. This simplifies the code in the Effects as they don't have to
keep track of the window they created any more. In EffectsHandler it
means that only one window needs to be created, destroyed and raised.
Also it means that we can properly react on screen size changes which had
been ignored in the past. Also quite some roundtrips to X are no longer
needed as we do not need to query the window geometry when creating the
input window.

REVIEW: 110156