Allow download of all petition names

[aaronlifshin]

(This is a low priority issue)

There's a download button next to each petition, on the "petitions" page. it gives you the first 10k. so if we have more than 10k we'll usually just deliver by saying "these 10k people, and 7k more, have signed our petition urging you to.....". to pull all the names would require a direct query of the database.