rtl_433_mqtt_hass, take config from env vars & externalise mappings.

[maxlock]

This is a successor to the previous pull I cancelled. It allows you to configure rtl_433_mqtt_hass from environment vars, which can be overridden by cli args. Additionally I've moved the mappings out to a file so a user can maintain their own custom mappings more easily. I've added a Dockerfile that I use as it's pretty useful, and takes advantage of the environment vars. Lastly I've moved everything into it's own subfolder for clarity.

[maxlock]

I forgot to add that there is a small breaking change in that the --user argument is changed to --username to match --password which isn't abbreviated either. Additionally, it's easier to see the actual changes in the 2nd commit due to the way git decides whether a file is new or just moved.

[klattimer]

This pull request seems to change the entire file - so I have a conflict with it here https://github.com/merbanan/rtl_433/pull/1665

[pacc]

https://github.com/pbkhrv/rtl_433-hass-addons has a docker file that runs this as an addon in homeassistant / hassio but I'm more interested in remote controls and alarms so I'll look into klattimers patch first.