EPIC: research further analysis related features to add to the AOI functionality

[leothomas]

Eg: https://github.com/NASA-IMPACT/covid-api/issues/56

[leothomas]

Some ideas about further analysis items to include in the AOI functionality, from a discussion with Barry Lefer and Ken Jucks (Air Quality scientists):

Current:

• Mean of values within AOI
• Median of values within AOI

  Potential:

• Std. dev of values within AOI
• 25th and 75th percentile values within AOI
• 7 day rolling average
• 15 day rolling average
• % of valid data values within the requested AOI (eg: it might be useful to the user to know that the AOI they've drawn is actually half over a body of water for which there is no data)