User tracking and permissions/authentication

This pull request introduces two plugins:

* UserTrack: Keeps track of channel membership and freenode account name for visible nicks.
* Auth: Allows configuration of user permissions based on freenode account names, and a flexible approach to checking if a nick has a particular permission.

This should allow us to start work on op commands, e.g. topic changing, being able to rely on the freenode account identification.