Fix Physics Render Tests

The rigid body physics render tests were not working correctly. This was
caused by a change 13ab10ec2e5b31e8820194c78ac8e58a75e380f4, where the
rigid representation's state was set on doInitialize instead of
doWakeUp. If the pose of a an element being driven by a rigid
representation was set after doInitialize (as is done in these render
tests), it would be overwritten the first time the rigid representation
is updated. This change, put the setting of the rigid representation's
state back in doWakeUp so any changes to the scene element pose before
wakeup are accounted for.
Merge branch 'fix/physics-render-tests' into 'master'

Fix Rigid Body Render Tests

+1: Ryan Beasley, haizhouW

Merged-on: https://www.assembla.com/code/OpenSurgSim/git/merge_requests/1060003
Fix sign compare warning in NamedDataPerformanceTest.
Merge branch 'fix/namedataperformance-sign-compare' into 'master'

Fixes signed vs unsigned comparison in NamedDataPerformanceTest.

Merged-on: https://www.assembla.com/code/OpenSurgSim/git/merge_requests/1071003
Fix bug + typo in RigidRep::addExternalGeneralizedForce + update doc

The rotation matrix is computed from angle/axis with
R = cos(angle).Id + sin(angle).skewMatrix(axis) + (1-cos(angle)).axis.axis^T
axis.axis^T is not the same 3x3 matrix as skewMatrix(axis)^2...there is a identity matrix difference when axis is normalized...

Many documentation on the web gives you the wrong formula, using skew(axis)^2 instead of axis.axis^T. I added a reference to a proper definition on wikipedia.
Handle case angle~0 in RigidRep::addExternalGeneralizedForce

When the rotation is close to identity, the angle gets closer to 0...and some terms become undefined.
A limited development of 1st order is used in this case:
sin(angle) ~ angle
This is used to simplify the equations and get the result.
Extensive Testing of RigidRep::addExternalGeneralizedForce

+ Test both methods (application point on the mass center or not)
+ Test that the method taking potential stiffness/damping matrix works as expected when these parameters are present or not.
+ Test extra torque + extra terms in the derivatives
+ Test full case with a full spring-damper (same type as the VTC)...verifying that a numerical evaluation of the derivatives is equal to the formal calculation.
Merge branch 'master' of git.assembla.com:OpenSurgSim into feature/reviseRigidExternalForceDerivatives