Add temperature settings

Hi @kirienko , Thomas had requested the following:

- set and read gas temperature: this is done by the TMP command
- related to the temperature one also has to set the scale (K or °C) with the TSC command
- return the properties of the selected gas: VIS, TCO, AMU. You have implemented the feature to change the gas (probably with the GAS command) and to set these values from the table. Would it be possible to just read VIS, AMU and TCO to readonly device parameters? This is kind of a sanity check. Or do you think this is not useful?

This MR adds this settings. I've asked Thomas for feedback. In the meanwhile, could you please have a look, and tell me where there should be more comments?

Thanks dude!