relax SVN archive

Added a print out to the centre() function.

The calculated paramagnetic centre is now being placed into the current data pipe.

Added a missing import and fixed an incorrect reference to the data pipe container.

Shifted the calculation of the paramagnetic centre from __minimise_setup_pcs() to centre().

The data pipe arg is now accepted by the centre() function.

Added the pipe arg to the pcs.centre() user function.

Wrote the num_data_points() method for determining n.

Wrote the model_statistics() method.

Bug fixes and expansion of the __linear_constraints() method.

The bug fix is that the b array was not being scaled! This is essential when diagonal scaling is
active.

The added feature is that the pN weight of state N, which is not a parameter of the model, is now
constrained to be between 0 and 1. This is because the value is equal to 1 minus the sum of all
other probabilities, hence linear constraints can be created.

Added the ability to reload alignment tensors from the XML results file into the relax data store.