Allow Actions to return results (Result Object in ActionResponse).

Adds an Object result field to ActionResponse, so Actions can store
a result there.
The field is intended to hold the result of the execution
when execution has finished successfully, and should be null otherwise.
Even when an action has been executed successfully, its result may be null.
Merge pull request #644 from isartcanyameres/feature/action-returns

Feature/action returns