Elexon B0620 & B1620

[fjebaker]

Added flows for scraping

• B0620: Day ahead total load forecast per bidding zone
• B1620: Actual aggregated generation perType

In the SLIMJaB code, the B1620 data is never used as is, and is always aggregated. Infact, the incoming data for B1620 is pretty degenerate, so I put the aggregation functions directly into the flow, and then we store the total quantity in a given period for every resource, per row in the database.

Screenshot

Note the flows are starting to get a little messy, so I think we should open an issue about tidying this into sub-flows, so we can abstract common reused sections.

[fjebaker]

Note these new tables also cylce on the 24 hour period.