HTTP API to reflect control socket API

[raybejjani]

Mimic the control socket API so that in-browser UI elements can also manage the daemon. It's likely that the web components will do more than the CLI tool but parity between both would be nice. Example API sets could be:

• list/add/remove a local repository from this daemon's watch list
• SHAs for all branches for a given peer
• Which branch/SHA is checked out by a given peer
• diff of two SHAs available locally