CCS811 Reference Baseline Management

[nicpom]

At present, SCK reads the latest CCS811 baseline when device is powered OFF, and rewrites it after power ON. The same action is performed during hardware reset.

A better management could be implemented, where a "reference" baseline is maintained in non volatile memory. This would allow the user to calibrate the sensor placing it in a clean environment, and saving that baseline, thus protecting it by accidental deletion due to uncontrolled power down. It would be useful to restore the sensor to a known condition in case of doubt on current baseline.

The procedure of saving the reference baseline could be implemented with a combination of hardware buttons.
Similarly, the reference baseline writing should not be the default action after power cycle, but should be selected with some additional action on hardware buttons because, in normal conditions, the sensor internal baseline management should be preferred.

[bryn51]

I suggest that it is better to implement the procedure to saving of a baseline by way of the CLI, rather than button combination. The reason I say this is that when the kit is deployed inside a smart citizen station, the data board is mounted deep within the enclosure; requiring a disassembly to get at all of the buttons. Only one button is available externally. It is of course possible to attach a set of buttons, but that brings about other challenges (namely finding a grove socket to attach them to).
Whereas implementing a new CLI command is relatively simpler (edit of command.cpp etc)