Added claim code printouts.

These don't quite look as awesome as jess' mockups, but they do contain
all the required information.

Note that the `OPENBADGER_CLAIM_URL_TEXT` environment variable must
be defined in order for the handouts to have a URL on them; otherwise
they just say "go to the website" rather than e.g. "go to csol.org/claim".

I believe this fixes #184.