[enhancement] Add current water year data as a supply scenario

[jessejanko]

For basins with available supply data, the current water year should be a selectable supply scenario. Previous months' data would be firm, while future data would be statistical flow projections (e.g. 1st, 25th, 50th, 75th, 90th percentiles). TBD which projected percentile should be there if we can only show a single data series, but here's an example plot:

Implementing this will require the development of an automated process to ingest past months' data from CDEC and projections from B120 and CNRFC on a ~monthly basis to update the input datasets. Here's a narrative description of the required data processing steps:
SupplyDataProcessing.docx