Smoke and overtemperature sensor for 2020 extrusion

This is a more elaborated detection unit to be mounted on critical places in the printer like
- Electronic box : detection of smoking/burning heated bed connectors, failing cheap PSU ...
- Printing area (enclosed)

The unit has an FC22 print with a gas detection unit on it like the MQ135 ( suitable for detecting of NH3,NOx, alcohol, Benzene, smoke,CO2) , an NTC for overtemperature detection and a LED to signal fault conditions.
See detector specs [here](https://www.olimex.com/Products/Com