Expand site extraction logic

[nocollier]

Definition of Done: We can execute ilamb run on a Fluxnet configure file from Jitu and have it run against ELM NGEE site runs and have it pick the correct nearest cell in the analysis.

Currently, when comparing two sources that are gridded and point data, we select a grid cell which is the closest (Euclidean distance in lat/lon) to the point data. In order to better use point data, we need to expand this notion to allow different selection criteria.

[msteckle]

Jitu is thinking this could be testied Ameriflux GPP data with dominant PFT cover type