[P103] Add support for EZO-HUM sensor

[tonhuisman]

From a forum request.

Features:

• Add support for EZO-HUM sensor
• Initial support for EZO-RTD (thermo sensor) and EZO-FLOW (flow meter) sensors
  (disabled for now, as these are in UART mode by default)
• Allow configuration without a sensor connected
  • Select sensor-type based on I2C address if no sensor connected

TODO:

• Finish configuration options
  • Options for HUM sensor
  • ? Options for RTD sensor
  • ? Options for FLOW sensor
• Testing of EZO-HUM sensor (help wanted, not available here...) (preliminary success, more fixing to do)
• Update documentation

[tonhuisman]

@kretzp I've done an attempt to add support for the EZO HUM sensor.
Can you please verify if the other sensors still work as intended with my mods?