MYST3: Don't open the executable several times on startup

This can be slow, especially if decompression / decryption is needed
MYST3: Build the zip-bit index at runtime

It can differ between versions
VIDEO: Fix Timestamp API usage in Bink seek code
MYST3: Adjust movie frame counts given by the scripts according to the framerate

The Xbox version making of video is 29fps instead of the usual 15
MYST3: The cursor tables are different for the Xbox version