API should automatically invoke lifecycle handlers for triggers tied to feeds

At the moment, the CLI handles invoking the CREATE and DELETE lifecycle methods for feed actions, when using wsk trigger create/delete.

@starpit tripped over this when managing triggers via the API.

I claim that the logic to invoke feed action lifecycle methods should be lifted from the CLI to behind the API, as a first-class aspect of the programming model.

Start by locating the CLI implementation behind `wsk trigger create/delete` and its CREATE and DELETE lifecycle handling, then trace the corresponding API trigger path. Done means feed action lifecycle methods are invoked through the API as a first-class behavior, with the existing CLI behavior still working.

Written by the indexing model from the issue text.