Add external force/stiffness/damping accessors in DeformableRep

This is to be compliant with the RigidRep API
Fix filename FemRepLocalizationTest.cpp to Fem3DRepLocalizationTest.cpp

This file is testing the Fem3D localization...it was wrongly named.
+
quick clean up
Add Fem1DRep/Fem2DRep Localization + UnitTests
Implement Fem1DRep/Fem2DRep addExternalGeneralizedForce + UnitTest
Clean all Fem based doCalculatePosition method
Clean up all Fem based addExternalGeneralizedForce

ASSERT on all parameters (nullptr and expected sizes)
But do not need to assert on further information contained inside the Localization (index/coordinate), the Localization class took care of that part.
Clean up all Fem based Localization doxygen doc
Remove all Fem Localization default Ctor + Ctor now take both Rep and Coordinate

setLocalPosition remains accessible if we need to change the local coordinates on the fly.
This method runs all the necessary checks to guarantee the proper functioning of the Localization, so it is safe to use it.
Merge branch 'master' of git.assembla.com:OpenSurgSim into feature/fem1d-2d_AddExternalGeneralizedForce
Merge branch 'feature/fem1d-2d_AddExternalGeneralizedForce' into 'master'

Add Fem1D/Fem2D addExternalGeneralizedForce

Merged-on: https://www.assembla.com/code/OpenSurgSim/git/merge_requests/1073503