Consider offering gzipped Full JSON as an export type

[kerchner]

Compression on Full JSON is roughly a 1:8 ratio, so on a large extract (such as an extract from Sample Stream), providing the export gzipped could make transfer much easier. Consider applying gzip as an option (perhaps a checkbox?) that could apply to any export type.

This came up in the context of preparing for Prof. Broniatowski's class, EMSE 4197, as we would like to offer students the option to export data from the Twitter samplestream; these exports can be quite large in their raw, non-zipped, form.

[lwrubel]

Discuss with @justinlittman whether to gzip all the files together or gzip individual files. Priority is full JSON export type.

[lwrubel]

For this ticket, gzip individual files, not the whole set of export files.