Updates to TileEntityRift

1. Fixed the bug where the setting that controls whether Endermen can
spawn from rifts was being ignored. It was never checked at all.
2. Cleaned up some formatting and annotations.
3. Removed call to World.removeBlockTileEntity() following a call to
World.setBlockToAir(). The latter function already handles removing the
tile entity.
Improvements to TileEntityRift

1. Removed several fields and functions referring to the newer rendering
code. The functions were just cluttering up the code and the fields were
consuming additional memory that was never being used for anything.
2. Updated NBT reading and writing functions to give some tags proper
names and to remove references to unused fields.
Removed the tag for riftCloseTimer because it was unnecessary alongside
the shouldClose flag. If a server reboots while a rift is closing, the
rift can start over upon reloading.
3. Renamed some fields and functions to have better names.
4. Changed the various checks for closing rifts. There were a few
redundant parts. We don't have to put calls to "this.invalidate()"
everywhere on top of explicitly removing the tile entity and destroying
its block.
5. Rewrote update timing checks. The rift spread and Enderman spawning
calls have been separated to distribute the impact of updating a rift.
Also, a flaw in the timing logic meant that the calculations for
particle offsets would only run when a rift was first created. That's
been fixed.