Make AppChooser 5x4 and less dense

Cells are now 128x128 so there's room between them.
While we are at it we resize it to 5x4 cells.
Add application information to windows

Properly configured windows has a class that contains the desktop entry
file name so we read it with QApplicationInfo and make it available
as an attached property.

Issue: #42
Emit a signal when a window is activated

This is useful for the windows switcher but might be useful on
a other places as well.
Windows switcher overlay

Overlay to switch windows.

Issue: #42
Move and resize when clicking on a subsurface

qtwayland will soon have subsurfaces support and with this patch we
can move and resize windows on Hawaii.