ZVISION: Use VideoDecoder facilities better in AnimationNode

setEndFrame() will ensure the audio stops when it is supposed to. Also removes the hack of retrieving the frame rate through the getDuration()'s timestamp return value.

Thanks to md5 for testing
ACCESS: Fix DisposeAfterUse flags in sound code (thanks to fuzzie)
ZVISION: Document some more controls
DEBUGGER: Extend the md5 and md5mac commands to handle any chunk length

This will be useful in matching the MD5 checksums with what the
advanced detector returns
ZVISION: The fist control is only used in one location
ACCESS: Remove useless variable
ZVISION: Make the rest of the controls properly use VideoDecoder timing

The hacky use of getDuration() to retrieve the framerate() is gone

Thanks to md5 for testing (and for filling in a few gaps since I was coding in the blind ;))
CREDITS: Update credits for ZVision again
ZVISION: Show system messages when subtitles are disabled

Thanks to Marisa-Chan for spotting this
Merge https://github.com/scummvm/scummvm