relax SVN archive

A lot of fixes for the internal structural object for handling multiple models.

The positive and negative cones from the frame order theory are now different PDB models.

Clean up of a RelaxError print out.

Fixes for all the renamed private methods in the internal structural object.

Created the add_model() structural API method.

This is implemented within the internal structural object.

Created the test data for the iso cone, free rotor frame order model.

Shifted the add_molecule() method to the correct position.

All private methods have been renamed by replacing '__*()' with '_*()'.

Added MC sims to the Frame_order.test_cam_rotor system test.

This is just a quick check with 3 simulations to make sure the code is functional.

Added Monte Carlo simulations to the second rotor frame order model testing script.

This is to check that the PyMOL representations are correct, as this cannot be done in a system
test.