WIP - Added download as CSV

Created by: jpic

This is a work-in-progress branch to offer CSV download of filtered representative lists. It adds a "Download as CSV" link next to the search form. It was tested manually that it preserves group and search filters, however I would like some time to add automatic tests.

Note that it doesn't use streaming response, because I'm still studying how to do that properly, but we can at most download 750 MEPs should it doesn't prevent using the feature for now.

The number of queries should be OK, but it has not been tested with assertNumQueries, again I'd like some time to test it, if possible.

Because it's in the "pr" branch, it's automatically deployed on http://pr-memopol.rhcloud.com/ which makes it usable for our friends who like spreadsheets right away even before the final implementation is merged ;)