Implement device node registration
This is the device node registering with the PiBox server.
- Device node must be configured for local network first (that's already implemented)
- At boot, the node sends a multicast message advertising its device type and version. It's IP address will be available from the multicast message (I think).
- The PiBox server picks up the multicast message and calls back to the Device Node using it's RESTful api.
- This requires an additional thread in piboxd to pick up the registrations on the multicast address.
- The device node configures itself appropriately and disables the multicast messages.
I need to define what it means to be "registered". Registration should also only occur when a user enables it on the server so we don't have random registration of rogue devices.