Helper for tweaking component behavior via node metadata

[bergie]

Node metadata is already passed to the getComponent method for instantiating components. We should implement a helper to tweak component behavior with this mechanism. This would allow graph designers to tweak at least:

• Control/triggering ports
• Bracket forwarding rules
• Throttling behavior (see Back pressure in Process API #581)

Since this will have to be integrated into existing components, we need some indicator in the component on whether it allows this kind of tweaking or not.