Issue correct message for SAML Status responses

[rhoerbe]

SAML defines a set of conditions that allow to pass exceptions, such as misconfiguration or authentication failures. Meteor should understand these conditions and use them for logging and display them instead of "TypeError: Cannot read property 'toString' of undefined". Such a message could be for example:

<Status>
    <StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Responder">
        <StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:AuthnFailed" />
    </StatusCode>
    <StatusMessage>Authentication failed. Error id [urn:uuid:0391278a-b19e-4b96-9529-45efcc2739f1]</StatusMessage>
</Status>