Added set_grid_values method to EmptyPort.
Refactored register_component_class.

Changed
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* Refactored register_component_class to use __import__ function rather than the imp module. It's much cleaner and probably more stable.
Added an update method to ChainEvent.

Added
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* New update method is just an alias for the run method.
Changed to use new framework.services functions.
Changed so that ports can be either strings or port instances.
Removed unused imports.
Added  PassEvent class as an empty event.
Updated sphinx rst doc files.
Added doctests and docstrings.
Renamed from pass.py to empty.py since *pass* is a keyword.
Changed to be able to create an empty manager.