[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.
The map is not just for ASF - it was intended to hold conversion info for several codecs (that's why the map also has a generic name and the section for asf/wmv has a comment). But if you prefer separated maps for each codec I'll change it accordingly (and rename the map as well)