MQTT room presence detection

[mKeRix]

Description:
This a component for detecting the indoor location of devices with MQTT clients. I have written a sample app at https://github.com/mKeRix/room-assistant (documentation incoming). Basically this component looks for all subtopics in room_presence (or what is configured manually) and then uses that subtopic as room name. The JSON payload (documented for hass.io) is then checked for the id and the distance, where the closest distance will be used as current room. If a scanner stops reporting the device the last distance is on a timeout.

This is fairly cool because it allows us to e.g. turn the lights on/off based on if someone is actually in the room opposed to just being able to control the general presence of being home or not_home. A wearable beacon in combination with a couple RPi 3 make it easy to track anything within the home.

Related issue (if applicable): none

Pull request in home-assistant.io with documentation (if applicable): home-assistant/home-assistant.io#810

Example entry for configuration.yaml (if applicable):

# Example configuration.yaml entry
sensor:
  platform: mqtt_room
  device_id: 123testid
  name: 'Cool device'
  state_topic: 'room_presence'
  timeout: 5

Checklist:

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.io

If code communicates with devices, web services, or a:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• New dependencies have been added to the REQUIREMENTS variable (example).
• New dependencies are only imported inside functions that use them (example).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.
• New files were added to .coveragerc.

If the code does not interact with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.

[mKeRix]

As discussed with @balloob I converted this device tracker into a sensor to avoid custom core changes.

[balloob]

Wouldn't this always be updated to the last updated time of the state ?

[balloob]

⚠️ Can't do this. You will delay all tests ever with 7 seconds.

[balloob]

Looks great 🐬