Upgrade to March Hare

This upgrades to March Hare (neé HotBunnies) 2.7.

Most of MH is backwards compatible all the way to the version we were using (1.5), but I had to rewrite a few things around subscriptions that's been changed: there's no longer a separate subscription object, but the consumer has all the properties needed (and really, the consumer is the subscription). The base consumers that ship with MH are also different so I needed to upgrade Autobahns custom consumer to use another base class.