Edward now reports: clear are sigs not supported

Edward now reports: clear are sigs not supported

Previously, if a user tried sending edward a message using clear
signatures, edward would reply that the signature could not be
validataed. This is because supporting clear signatures is quite hard,
partially due to mangling that an MTA might perform on white space in a
clear signed message, along with other issues.

Now edward lets the user know that it does not support clear text
messages. This should prevent user confusion under this scenario.
Currently this message is shared in english, even if the rest of the
response is in another language. Once translations are added, this issue
should be mitigated.