clock: Dont use deprecated rsvg_pixbuf_from_file_at_size

This required to copy some code from GTK3 source to make it working with GTK2 too

Thanks to Sander Sweers for the help to replace rsvg_pixbuf_from_file_at_size
gtk3: set rgba visual for applets
Fix for real transparency
Fixed all background issues with composited window managers.