Drop MP3Codec/libmad from paplayer and dvdplayer in favor of FFmpeg

Follow-up to https://github.com/xbmc/xbmc/pull/4386 and initially started by @fritsch - this drops libmad and MP3Codec stuff from paplayer and dvdplayer and rather utilises ffmpeg. While this removes a rather dated dependency (libmad was last updated 2004), the mpg123 decoder inside ffmpeg improves playback of MP3 audio files not being 100% compliant and might play back (partially) distorted when using libmad.

Linux should be fine. OSX (Xcode 5.1) 32bit build tested and working. Win32 project changes need review and testing. Other platforms need to be tested, too.

Probably only for G+1.

Credits belong to @fritsch who started the work :)