Refactor authz roles

[dread]

Suggestions from rgrp:

• Get rid of Roles, and replace them with direct assignment of actions, even though there are many actions, and extensions can add arbitrary ones.
• Debatable whether we should cut the number of actions to correspond to the three roles defined by the base system.
• Have a method of finding roles (or, in future, actions) relevant to a given protection object (e.g. FILE-UPLOAD(ER) not relevant to Packages)

(This ticket is split off from #1065)