Fixed minor stuff in ChTriangleMeshShape
Added the method Set_A_Xdir for setting a rotation matrix by passing a direction, with Gram-Schmidt orthogonalization (previously this required calling the same function, but in ChVector, and it was more typing..)ù
Improved ChTriangleMesh geometry class.
New class for converting FEM stuff into visualization assets. Still experimental.
Improved FEM code.
Now all elements are corotational, including the hexahedrons.
Also, few bugs corrected.