relax SVN archive

Spun out some of the minimisation code into the minimise_setup_tensors() method.

Fix for the model arg of the n_state_model.select_model() user function.

Created the setup_model() method so that the model parameters can be set up by numerous methods.

Fixed the model checking in the minimise() method.

Added some error checking for the validity of the selected model type.

System test fix for the renaming of n_state_model.setup_model().

Renamed the n_state_model.setup_model() user function to n_state_model.select_model().

This is to match the convention of the other analyses.

Docstring and print out fixes for the n_state_model.select_model() user function.

Fix for the n_state_model.select_model() user function.

Created the new error class RelaxNoModelError.