* Added active_gateway list to Session to support push/pop of current outbound gateway (future use).
* Added Mock Workflow 2 to test DecisionGateway -> FirstGateway routing selection (dynamic selection).
* Simplified (organizationally) several item-from-list lookups in engine via .pop() use.
* Shortened current_element to current in get_next_element.
* Renamed next_element to following in get_next_element.
* Functions get_next_element, get_current_element now use next() between operations (was: list()).
* Renamed gateway_make_decision to evaluate_decision_gateway.
* Code interpretation in evaluate_decision_gateway has been refactored to evaluate_gateway_paths.
* Function evaluate_broadcast_gateway stub created for eventual broadcast routing.
* Kickstart tornado stdout logging is now disabled.
* FileStore now performs atomic writes via 2-phase write -> rename.
* FileStore performs fewer encode/decode calls.