Revert "Revert "Introduce flowSpawnedBy handler to forward events from outside of FlowComponent""

Now with improvements and 100% more reverts!

This reverts commit 84b31b72d47e573bf1493387e6b1ebd3cad315e9.

Change-Id: I7fe9fb73645f9ecc99d0a474d63535fe3b14b7b3