Redirect to dashboard if there are no benefits to edit.

The sponsor object has been created, and we only need to collect details
about the potential-sponsor's benefits. If there are no benefits, the user
should be redirected to the dashboard rather than forced to submit what
appears to be the same form twice.
Merge pull request #49 from pyohio/pyohio-sponsorship-redirect

Redirect to dashboard if there are no benefits to edit.