[3D] add support for stereomode detection of other codecs than MKV

This PR is abstracting the stereoscopic detection to a separate function and is adding stereoscopic detection for wmv/asf files (see http://www.3dtv.at). Not sure if this is the correct way to go, so @elupus please have a look.
not sure what you mean? In which way is this method not generic? The CodecModeToVideoModeMap can contain conversions for different codecs - or do you want each codec to have it's own map?