Force all dimensions to share map storage. Fixes #182, #279, #284, #321

Due to the new world structure that CB has setup with environments, new
savehandlers were being created for each world causing different
mapstorage objects to be used in each dimension. This caused Mystcraft to
not be able to find the correct agedata. To fix this, I have adjusted the
initial patch put forth by forge to make sure all dimensions share the
same mapstorage object as overworld.