* Split the SGP30 baseline into 2 values
- According to the SGP30 datasheet, each eCO2 and TVOC baseline is a 2-byte value (MSB first)
- The current implementation ignores the MSB of each of the value
- Update the schema to allow 2 different baseline values (optional, but both need to be specified for the baseline to apply)
* Make both eCO2 and TVOC required if the optional baseline is defined
* Make dump_config() looks better
