Integrate weighting

[aaTman]

Currently, there's no API to include a form of weighting to EWB. There are a few immediate use cases that would benefit users, including:

• Area weighting
• Population weighting
• Custom weighting filters

This should be a fairly easy addition to the current approach. The biggest open question that comes to mind is at what point, exactly, to inject the computation to minimize either graph growth or a complicated implementation.

[linear]

EWB-51 Integrate weighting

[nicholasloveday]

@aaTman , if it helps, the recent scores version has an aggregate function for calculating weighted means (for metrics where you don't use scores). See the "weighting data directly" part of the tutorial here https://scores.readthedocs.io/en/stable/tutorials/Weighting_Results.html