Alcove v0.2.7

Show Desktop no longer makes the desk blink, and Alcove stops using a CPU core while idle.

Pressing Win+D used to flash the desk for a moment. Alcove was being covered by
the desktop and shoving itself back on top; it now sits with the desktop instead
of fighting it, so there is nothing to shove and nothing to flash. This holds
after restarting Explorer too.

Alcove also kept one CPU core busy doing nothing. Reading the colours out of your
wallpaper got stuck in a loop that repeated forever in the background. Fixed.