Edited Joint Descriptions
added gif's
addressed Sherms comments
spelling, links and what not.
Typos and the like
Merge branch 'master' of https://github.com/opensim-org/opensim-core into jointDoxygen

Conflicts:
	OpenSim/Simulation/SimbodyEngine/Joint.h
Merge pull request #257 from opensim-org/jointDoxygen

Doxygen description edits for Joint, including new gifs