[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.
Drop this wrapper, no fallback like proposed can be done in demuxer.