This was incomplete and just ignored Duke's special music, and the levelnum generation used an outdated formula so that it never managed to assign any music to the maps.
Since the decoder cannot handle sound, there's two options:
1: Use the same sounds as the video it replaces.
2: If an identifiable streamable sound with the same base name is found, it will be played along with the video.
Fixes#133
* moved Smacker video playing code into the backend, so now all games can play all supported video formats
* logos and level intro/exit videos use ScreenJob
