ZENGINE: Rename 'x' variable in changeLocation to 'offset'

Since it can be in either the x or the y direction
ZENGINE: Modify cmdLoadSound to allow manual rate and isStereo

Usually those variables are parsed from the file name
ZENGINE: Render images by specifying a destination and then clipping

Instead of specifying a subRect. This also reverts the code that rendered to a
backbuffer and then did a full backbuffer warp. Wrapping is done in the RenderTable
ZENGINE: Set the background position after the .scr file has been parsed so we know the RenderState
sound asdf
ZENGINE: Modify cmdLoadImage to match new render code
VIDEO: Add AVI LIST handling for ZEngine custom types
ZENGINE: Re-enable video handling now that AVI code is fixed