EMI: Refactor handling of materials, fix texture animations

These patches make sure that there is only one instance of each material per instance, and fix the lookup of this instance by file name. This fixes a number of texture animations and effects, including:
 - Water and lava animations (broken by 70520e5)
 - Blinking
 - The various looks of the pirate caricature
 - The look of the blue painting when Guybrush is holding it

Unfortunately the blue painting still looks wrong in the inventory because the chore that is supposed to select the correct texture is immediately cancelled when the actor is put into overworld. I'm not yet sure how to fix that.