Wallpaper Plug

A simple wallpaper choosing pane for switchboard. Figure I'd fix it up a bit since its now part of a larger plug. The cog on the wallpaper thumbnails will give a menu to edit the zoom options like center, crop, etc. And selecting multiple wallpapers automatically gets you multiple backgrounds.

TODO:
# Option to change the time the wallpaper is on the desktop before moving to the next one.
# Select all/deselect all modebutton