Correct a decimal, add host to redirect

* Updates a test to use more realistic form submission data
* Fixes error which resulted in payments from pay.gov in cents rather than dollars
* Adds scheme and host to the redirects after a successful donation

Note that we'll need to test the redirects in our demo environment -- we need to verify that the host in our configuration is the one that users should see. If not, we'll need to rewrite this.