#75 recognize mka/mkv/mk3d as audio/video

[Arnout Engelen]

The following could be added to config/mappings.xml :

<map from="mka" to="audio/x-matroska"/>
<map from="mkv" to="video/x-matroska"/>
<map from="mk3d" to="video/x-matroska"/>

I haven't tested mka or mk3d, but this makes my Philips 32PFL9705H TV to play some mkv video's properly.