Add support for BLE meat thermometers for less soldering

[bobpaul]

This was described in a comment on #149, and I thought it would be a good idea to add it here so it's not forgotten:

Basically the idea is use a cheap BLE meat thermometer with several inputs ( @faisalhusain007 mentioned one with 6 probes for $20 ) as meat thermometers to PiFire. Someone could use this in a build instead of using the onboard ADC. PiFire would then make the values available via its webapp and use them for cooking modes that utilize the meat probes.