Use weight data from all 3 bars / load sensors

[DanielleSucher]

This will have to involve a few changes both on charcutio and charcutio-web.

Currently the local script only registers one weight sensor to send to the server. It should change to accept 3 weight pins, register 3 weight sensors, and send all 3 to the server with different names so they can be graphed separately.

On the server, there needs to be some way to identify which weight sensor's data goes with which meat, or at least which goes with the master meat, so we can track the moisture content of the meat and thereby adjust the humidity setpoint and determine doneness.

The simplest way to do this may be to name them 'master_weight', 'weight2', and 'weight3', and on the server, and then track everything through 'master_weight' DataPoints and the master_meat object for each box.