Use last_modified timestamp to save database query results

[shansen5]

With the last_modified of the database tables we can store CSV files of database query results and use them in subsequent runs for faster responses.
When asked for a data set we can check a date stamp on the CSV file and query the Last Modified table to see if our CSV still contains the most current data.
Using data from a local CSV will be faster than downloading results from the database.

[Frijol]

@shansen5 is this still relevant?