WIP: Stats endpoint

This WIP branch will fix #152 when completed.

The following should be implemented before the branch is merged with develop:

* The stats access event listener should be able to handle wildcards in the IP addresses in the white-/blacklists.
* The stats model should have a simple `key => value` container that event listeners can use to inject custom statistics.

Any other features that should be added? 

Oh, BTW, this pull request also removes support for the HTML media type. I didn't bother putting this in a separate pull request.