EMI/GRIM: Nothing should be visible if actor is not in current set

When fiddling with the controls in the Palace of Prosthetics Guybrush is
temporarily put into set "nil". No items should be visible to him in this
situation.
EMI: Flip y coordinate when creating screenshot textures

The MakeScreenTextures() opcode is used to create texture tiles from the
current screen content for use with an overworld actor, e.g. when fading over
the slides in the intro. With OpenGL the created textures were mirrorered in
y direction because OpenGL uses a different coordinate system where (0, 0)
is the bottom left corner.
EMI: Fix rotation of overworld actors
Merge remote-tracking branch 'inguin/emi-freeze-frame'
Merge remote-tracking branch 'inguin/emi-fixes'
Merge remote-tracking branch 'inguin/emi-overworld'