Read uploaded CSV into MongoDB collection

Related to:

• #19 internal data sources
• #37 (closed) filtering for CSVs
• #45 (closed) POST to internal data sources

Data uploaded as CSV should be stored in a MongoDB collection to allow it to be sorted. Inferring data types is not essential if the only comparison is equality, but inferring numeric types is easy and would allow proper sorting. Other types can probably be left as strings.

MongoDB is present already for PROV storage, and allows the flexibility required for general CSVs (e.g. don't need column headers, different numbers of columns per line)