Use single data source for workshops

[fmichonneau]

Currently, the plots for workshops are made from the raw CSV file, while the data feed used in our website is from a modified version that filters out workshops that don't include an URL. As much as possible these 2 data sources should be identical.

[maneesha]

I think our query is also doing an inner join of workshops & instructors (and therefore excludes workshops where instructors have not yet been recorded) while the AMY feed includes those workshops.