Plan/Engine: Filling in plan_ref for every maneuver.
Plan/Engine: Filling in maneuver's id before loading.
DUNE/IMC: Generated IMC after adding PlanMemento message.
Plan/Engine: Added class to handle incoming Memento messages.
Plan/Engine: Using new class MementoHandle to process incoming Memento messages.
Plan/Engine: Parsing PlanMemento when it comes as the arg of PlanControl.