Revert "Implemented spherical/cylindrical coordinates for velocities."

This reverts commit 485ee1886333affb3ed9ff91937c2cf852d7b4e2.
CORRECTLY implemented spherical/cylindrical velocity coordinate tracking.
Set up for consistently tracking velocities; need to get velocity vectors...
	modified:   hdf5.py
Bugfix.
	modified:   hdf5.py
Include density limit info in accretion disk database.
	modified:   sink.py
Stop being an idiot and creating a new table for every density limit.
	modified:   sink.py
Merge branch 'dev'