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?
This is the old format and it is backward-compatible with the old code (password field is just ignored). My argument is that giving consent on someone else's behalf is not a meaningful attack.
In addition to that, you don't need to verify the password for the informed consent since the only entities that know a client's username and typeable handle are the server and the client itself. Checking either of those is good enough for this kind of action.