Make engine configurable, make debugger show local variables

To make it easy to set Mistral for debugging.
1) Make engine configurable.
2) Enable debugger via command line. Passing --use-debugger will make PyDev or PyCharm show
 local variables in debugging session.

Also, a tiny fix in action_factory.

Change-Id: Id054ae5156649b1f6bbba7131e54bf21d71c659a
Merge "Make engine configurable, make debugger show local variables"