Use Google's Cloud Score+ to remove cloud pixels

[ejm714]

Right now, we only use a cloud screen to toss out images that have too many clouds, but then we calculate features from all the pixels in the selected image. A better way would be to actually remove the cloud pixels. Sentinel 2's SCL band is too lossy for this (throws away too much data). Google's Cloud Score+ is supposed to be much more accurate and fine grained so we should look into using this algorithm to drop cloud pixels before calculating features from band statistics.

https://developers.google.com/earth-engine/datasets/catalog/GOOGLE_CLOUD_SCORE_PLUS_V1_S2_HARMONIZED

https://medium.com/google-earth/all-clear-with-cloud-score-bd6ee2e2235e