Cylindrical Dirichlet boundary conditions can now be applied, using the keywords DISPLACEMENT_R and DISPLACEMENT_TETA. For now, only cylindrical coordinates with and origin of (0,0,0) and
a z axis (0,0,1) can be applied, which means that the structure must be oriented along the Z axis and centered on (0,0,0) (which should not be a problem for most of the cylindrical
problems).

It was chosen not to implement it for Octree computations, since Octree computations are performed on rectangular structures, but this could eventually be implemented if necessary.