Setup mgmt area for all the mgmt-type stuff.

This sets up mgmt as a proper, namespaced area with a dashboard (which still just lists the previous agendas for now).

**This removes the ability to update an agenda so it should NOT be merged until there is a corresponding pull request with a full Agenda management interface**

Just wanted to get this up here for code review and corrections before moving on to Agendas and Venues.