Rename Signal.get_deecopy_with_new_data to Signal._deecopy_with_new_data
Rename Signal.print_summary to Signal._print_summary
Remove HasTraits from Signal
BUG-FIX: Signal._check_signal_dimension_equal* were raising the wrong exceptions. Also remove some unused variables and imports
Rename some Model methods and improve curve fitting documentation.

* Rename Model.set -> Model.store_current_values
* Rename Model.charge -> Model.fetch_stored_values