Triggers should activate actions via internal interface

Currently a trigger causes an action activation through an external interface - but we should use an internal interface.

• refactor entitlement check to authorize action
• create internal interface for activation a trigger (useful to surface web triggers)
• replace http post request for internal interface
• restoring ability to track causality

Also consider as part of this some long needed changes to handing of triggers:

• persistence of trigger and/or rule activations https://github.com/apache/incubator-openwhisk/issues/512
• logging activation ids (or failures)