relax SVN archive

Created 3 new fns, get_molecule_ids(), get_residue_ids(), and get_spin_ids().

These return lists of molecule, residue, and spin ID strings.

The residues and spins in Mol_res_spin_tree are now only created if they are new.

Molecules are now handled differently in Mol_res_spin_tree if the already exist or not.

New molecules are added to the tree while old ones are left alone.

Split up the Mol_res_spin_tree.update() method into separate methods for molecule, residues, and spins.

The pipe.switch() user function is now only called in the spin viewer if a different pipe is selected.

User function completion now triggers self.gui.user_functions.notify_observers().

This will allow for GUI updates upon user function completion.

Created the on_completion() wizard method which is executed after running on_execute().

The spin view window is now registered to have self.refresh() executed when a user function completes.

Converted User_functions into a observer design pattern.

This will be used to notify the GUI that a user function has completed.

Added the structure user function menu to the spin viewer window.