relax SVN archive

Split up the n_state_model.model() user function.

The new user functions are:
n_state_model.number_of_states()
n_state_model.ref_domain()
n_state_model.setup_model()

Fixes for the read() function to allow the error column to be missing.

Made the error column optional in the loading of RDCs.

Converted the read() function from the relax_data code.

Created 2 new error classes, RelaxNoRDCError and RelaxRDCError.

Created a generic_fns rdc module by copying the relax_data module.

Converted all of the rdc user functions from the relax_data code.

Converted all instances of 'relax_data' to 'rdc'.

Converted all instances of 'ri_label' to 'id'.

Converted the rdc.read() user function from the relax_data.read() code.