use custom models for most doors

all are derived from homedecor's pre-mtg-doors models, with minimal changes,
so doors should look virtually identical to what they used to.

uses the old clone_node() technique to force-dereference the door defs

reworked a few textures for quality and to fix stuff I broke but didn't
notice right away, pulling from pre-mtg-doors when needed.

also fixes the broken alpha on doors that use it.