Store configuration details

A user may prefer to always use a particular set of default timings that differs from the standard set. Using GConf will allow the programmer-set defaults to be overridden with user-set defaults.

Configuration options will be located under /apps/crebs/:―

directories/images (string, user home directory)
directories/slideshow (string, ~/.crebs)

times/default_duration (float, 900.0);
times/default_transition (float, 3.0);

files/standard_output (boolean, False)
files/create_files (boolean, True)
files/force_overwrite (boolean, False)

wallpaper/register_wallpaper (boolean, True)
wallpaper/set_wallpaper (boolean, True)

notify/send_notification (boolean, True)