Allow specifying actions per controller

[vincentvanbush]

Currently, all named actions for the entire authorization configuration must be defined in a single actions file - this is not very convenient as, in Phoenix, it means that all actions from all the controllers you want to authorize have to be repeated and enumerated in a single file.

As of now it appears that the only thing this module is used for is distinguishing between singular and plural actions and action grouping.

We would like to do this instead:

1. Implement the singular_actions and action_grouping functions on a per-controller and per-live-view module basis instead of in the implementation of Permit.Actions.
2. What is now implemented by default in Permit.Phoenix.Actions should be moved to default implementations in Permit.Phoenix.Controller and Permit.Phoenix.LiveView, and just mad eoverridable.