add Download button

[gregallensworth]

Add to the nav bar at the top, a new Download link.

Option 1

A hyperlink in a new tab, to CARTO, containing the very same SQL query which is being used to generate the data, except with &format=csv added.

• Potential for very long URLs? An URL above 1000ish characters is not a good idea... Check into the queries and see how lengthy some of them get, whether any of them require using POST instead of GET.
• Best way to expose that raw SQL query to higher-level places such as the Application and thus the navbar...

Option 2

Create a false file download dialog of the data already in-memory from reselect. Could circumvent long-URL issues, and give faster performance.