* map [+baseattack] added missing clips to locker models in quarters.map
* cleanup in frozen.ump and +frozen mapdefs

* use tabs instead of multiple whitespaces
* more verbose names for map assemblies
* restrict +frozen to 'cold' environment, as we have +ice for 'arctic'
* map name should not imply aliens 'landed' or similar, we use it for crashed UFOs too
* map [+frozen] replaced the dropships by actual prefabs
* map [+frozen] cleanup
* map [+frozen] try to put some snow onto that roof