ZVISION: Plug a memory leak
ZVISION: Disable unused code
ZVISION: Introduce pixel formats for resources (555) and screen (565)
ZVISION: Let the cursor manager do pixel format conversion for cursors
ZVISION: Set all the internal graphics operations to use RGB555 (1/2)

This is the first part of the changes to make the engine use RGB555
internally again. This is done to simplify the rendering pipeline -
the engine will use RGB555 internally, but will output to RGB565.
The overall changes have been broken into two commits, thus this
first commit will break all the game colors
ZVISION: Set all the internal graphics operations to use RGB555 (2/2)

This is the second part of the changes to make the engine use RGB555
internally again. This is done to simplify the rendering pipeline -
the engine will use RGB555 internally, but will output to RGB565.
The overall changes have been broken into two commits, with this
commit finishing all the changes.

This is needed, as the game uses RGB555 graphics internally, but
its AVI animations (full screen and in-game) use RGB565
ZVISION: Plug another memory leak. Some cleanup