Improvements to TileEntityRift

Made some improvements to TileEntityRift. The main reason for these
changes was to remove the field nearestRift - we should not hold on to
references to links. Now we simply track the location of the nearest
rift. I also confirmed that closeRift() and updateNearestRift() must be
allowed to run on both the client and the server. If the client doesn't
run those functions, then adjacent rifts don't connect as expected and
the rift removal animation doesn't work.
Minor Change

Autocorrected indentation in PocketManager. I'll be working on changing
PocketManager to prevent the risk of creating data for a non-existent
dimension through a bad call to getDimensionData().
Fixed Crash on World Creation

Fixed an issue. DD would crash when MC created a completely new world
because onChunkLoad() would be called before onWorldLoad(). That's not
the usual order. PocketManager would be unloaded at that point and would
return a null dimension.
Merge pull request #174 from SenseiKiwi/master

Fixed Crash on World Creation