relax SVN archive

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.

Fix for the structure.load_spins user function window.

The 'combine_model' arg should have been 'combine_models'.

Another fix for _build_doc() for the handling of fn._doc_additional.

Fix for _build_doc() which was broken in the last commit.

_build_doc() now handles the fn._doc_additional structure for adding additional sections.

Removed the starting and ending newlines from the id_string_doc used as a tooltip in spin_id_element().