Remove `recipients' from campaign.

For now, we'll only be sending petitions, and we can just hard code
the recipients.
Adjust spacing between image and link in tablet view.
Change app name.
Fix wording.
Require campaigns to be created with an image.
Revert "Remove ability to sign up spontaneously."

This reverts commit 70b3d80fe34fc30230fd2564ce71907db94a063a.