Adds the AirVisual air quality sensor platform (#9320)

* Adds the AirVisual air quality sensor platform

* Updated .coveragerc

* Removed some un-needed code

* Adding strangely-necessary pylint disable

* Removing a Python3.5-specific dict combiner method

* Restarting stuck coverage test

* Added units to AQI sensor (to get nice graph)

* Making collaborator-requested changes

* Removing unnecessary parameter from data object