Actions on worker

This change adds the ability for Actions to be run on a charm using the
same logic used for Hooks.  The Action is run in the "actions" location on the
charm.

A second PR will address Action param Validate.
I agree with that, I think that might belong to the PR where I add ActionGet and ResultsSet -- should be the very next one on the list.  Not quite certain which file / package that type belongs in just yet.