DS18B20 Plugin

We need a plugin which will publish the temperature from a DS18B20 1-Wire temperature sensor.

This essentially implements DS18B20 to MQTT as a plugin.

I have the hardware to test it, so I can tackle this one.

Progress:

• Import existing project
• Update README.md (plugin and main)
• Support naming sensors
• Better Unique ID --> separate issue, broader scope
• Unit tests --> #15 (closed)