Support for codec interfaces partially implemented

batch_downloader and gtk_batch_downloader updated for codec interfaces,
added helper function for loading all available codecs, added theora and
vorbis codec(+ interactor between them), added ffmpeg_base_codec, that provides
boilerplate code for codecs using ffmpeg, updated glade file for options
screen(partially), updated options.py file(partially).

That was a big one, wasn't it?