added support for typeable URL in consent form (closes #29)

Removed password from the old consent URL (giving consent does not require password).
Also shortened the URL for the typeable version. This will be backward-compatible with the old clients (both URLs work). This will close #29.
@ben-jones, can you please review this?
If you wanted to get more use out of your display_informed_consent function above, you could refactor it to replace the username, then return the content. You would need to read the file before sending it to the function, but it would let you reuse functionality here.