REP-819 Keystone V3 Filter

The mess that is Keystone v3! Comment on _everything_ so we can get this fixed up. =)
Not sure what to do here. We construct a new FilterLogicHandlerDelegate each time, but handlerFactory.newHandler does always return the same handler. Alas, that's the pattern we have been using, and the method names are enforced by an interface.

This might be a matter of breaking the pattern (which I would like to do when we refactor this filter). Do you have any suggestions?

Also, to verify, we don't want to create a new handler for each request, do we? The only shared state is the cached admin token, but akka handles the case where everyone goes to fetch a new one. That is, if multiple threads attempt to overwrite that value with the value returned from the Akka client, all of the attempts will simply overwrite var with the same value, which is acceptable.