TileConstants: make isIndestructible()

continuing the trend of moving tile number logic to centralized location

git-svn-id: https://micropolis.googlecode.com/svn/trunk/micropolis-java@798 d9718cc8-9f43-0410-858b-315f434eb58c
experimental: define large zone structures in tiles.rc
experimental: use large zone structures defined in tiles.rc
experimental: use large zone structures defined in tiles.rc for COM and IND