Add ability to add controllers, document API endpoint

[blalor]

The kegbot admin page says Note: Controllers can be created and edited in the Kegbot app. This is not helpful if you're not using the Kegbot app. Please add a UI component to manage controllers and document the API endpoint for /controllers/.

[mik3y]

Acknowledged, this would be useful.

[blalor]

Here's what I came up with:

curl -X POST \
    -H 'X-Kegbot-Api-Key: <your_api_key>' \
    -d "name=<name>" \
    -d "serial_number=<name>" \
    -d "model_name=tablet-less, yo" \
    http://localhost:8000/api/controllers/

I took the name and serial_number from the output of kegbot_daemon.py:

2014-06-26 17:21:18,271 INFO     (main) kegboard-ABCD: <HelloMessage: protocol_version=None firmware_version=18 serial_number=KB-01xx-xxxx-xxxxABCD>

Once that's done you can add a flow sensor from the admin page.

[mik3y]

FYI, pycore now automatically creates a two-tap controller when a board is connected (new in v1.2). It's a partial workaround for this issue (which will remain open) but should handle the common case.

[mik3y]

Fixed in #364