Added MV support for Mystcraft. Fixed IC2 texture bug when using MV.

All forge dimensions will now be created in root with following naming
convention : world_environment

Twilight  -> world_twilightforest
Mystcraft -> world_myst
If you have existing Mystcraft dimensions, move them to the following location
world_myst/ageXX where XX is the age dimension.
If you create a new Mystcraft dimension, you will need to restart the
server so MultiVerse can pick it up. Make sure you force a save before
restart so the proper mystcraft agedata is created. All agedata is still
created in world/data/agedata_XX.