Initial Git server

One goal of the Cryptosphere is to support the Git data model, not just from a theoretical point of view, but closely enough that a 1:1 mapping between the Git protocol and the Cryptosphere is possible, to the point that we can actually use Git clients to manage content in the system.

To that end, the Cryptosphere will implement a full-fledged git server that understand's Git's smart protocol. The present plan is to give it a URL namespace on the "control port" for the web UI, however security needs (or other needs) might dictate running it on its own port in subsequent releases.

This branch tracks the work towards adding an initial Git server