Need to add ".csv" extension to downloads from query builder

[cezary4]

When you download a csv from the query builder on the website, it downloads as a file called "download". There is no extension on the "download" file so you have to manually go in and add ".csv" before you can open it up and view it as a csv. We should fix this by just adding in ".csv" to the download code so that it shows up as a csv when you download it.

@mhkeller is this a front-end code fix?