Fixing blur bug: Icons were not redrawn properly after blur effect

 * Blurred colors were mixed with icon transparency, so an icon
   redraw command is requested after removing the blur
 * An additional option to clear the icon area in case the mouse
   pointer is currently drawing the second texture icon
Merge pull request #50 from KanoComputing/blur-broken-icons

Fixing blur bug: Icons were not redrawn properly after blur effect