Wallpaper switcher with Dropbox support

This creates a profile which runs when the display is on and the launcher is running. It spawns two child processes that swaps wallpaper, syncs dropbox (using Dropsync) and turns off the display after the launcher has been on for a specific time. Notice that this will not swap backgrounds or update dropbox when the launcher in the profile isn't running or when the screen is turned off.

Variables:

%SCREENSAVER_MINUTES	Time in minutes before the script should lock the screen. If this is set to 0 then the screensaver isn't enabled.
%SWAP_BACKGROUND_INTERVAL_SECONDS	Time between swapping the backgrounds. First swap will happen instantly.
%WALLPAPERS_DIRECTORY	The directory where the wallpapers are placed.
%IMAGES_FILE_TYPE	The file type to look for in the directory.
%CURRENT_WALLPAPER	The currently set wallpaper, intended for making sure the same wallpaper doesn't show up twice in a row and for integration with other scripts.
%DROPBOX_SYNC_INTERVAL_MINUTES	Minimum time between Dropbox synchronizations.
%LAST_DROPBOX_UPDATE	System time in seconds for last Dropbox update, used to make sure that we don't flood Dropbox and possibly for integration with other scripts.