Added BacklashHingeJoint, which doesn't quite work yet.  Changed inheritance structure for all the joint classes.  BacklashHingeJoint doesn't break anything if you set backlash to 0, the default, so I am committing for now and trying another approach
Removed traces of logger
Corrected default values for the 'prop' arguments
Removed logger reference
Added more explicit pause/unpause messages
Passing "world" args to joints instead of "sim" args... for unknown reasons subclasses of ode.HingeJoint don't let you change __init__ arguments, and ode.HingeJoint takes a "world" arg.  So we must hack around it.
Added function to create "TransferBody"s.  A TransferBody is a body that has no mass and exists only to allow the stacking of joints.  I could not get backlash features to work correctly just by modifying the joints I already had, so this allows me to stack two joints together to create backlash by making one of the joints unpowered and using its hard stops.
Added "SpringyHingeJoint".  Allows you to create an unpowered hinge with spring and damping constants.
Adjusted system pressure from 2500psi to 2300 psi
Turned off collision detection for thigh and yaw links
Implemented backlash for all joints.  Yaw has 5* of backlash, the other joints have 2*.  This is sort of based on real life.
Added backlash instrumentation to the published values
Removed a whole bunch of unused code left over from copying SpiderWHydraulics
Re-set row_motion to actually rowing instead of just positioning itself to a point.
Added computation of angular error
Added instrumentation for backlash
Hooked up control loops so that backlash affects them
Set the control loop to only run at 200Hz instead of every sim time step.