New engine: Beavis and Butthead In Virtual Stupidity

This pull request adds support for "Beavis and Butthead In Virtual Stupidity".

- The game is completable
- I didn't test it on a big-endian system
- I haven't run it with Valgrind but with DrMemory which didn't give any worrysome warnings
- The PSX version is not supported; it uses the exactly same scene files but graphics, sound and videos are all PlayStation-specific

One thing missing:
In the air guitar minigame, support for saving/loading of songs is currently not implemented. The original uses Windows' file dialogs. I didn't come up with a good idea how to reimplement this. I guess it would be ok if the files can only be saved in the savegame path and not in other directories, so maybe some kind of simpler saveload dialog could be used, since the songs don't have sceenshots etc. and it would suffice to have a simple list of filenames.
This will then be added in-tree.

I'm looking forward to your comments and suggestions!