Add translations for Air quality sensors.
Many devices have a textual Air quality sensor. Standardise the values
for those with mappings to the following 5 values so status can also
be translated:
excellent, good, moderate, poor, severe
Generally this meant the following changes:
great -> excellent
fair, mild -> moderate
medium, mildly polluted -> poor
Although the last one may seem to fit moderate better, for some
sensors this was the most severe reading they had, for others there
was a severe (literally from the device), so a less extreme negative
seemed more appropriate.
Issue #1708