Support more decimal places for seconds

[jalan]

OneLogin_Saml2_Utils.parse_SAML_to_time currently supports two formats:

• %Y-%m-%dT%H:%M:%SZ
• %Y-%m-%dT%H:%M:%S.%fZ

We're seeing Azure AD send timestamps like 2019-06-26T14:19:51.2123335Z in its SAML responses, with seven decimal digits. This is odd, but some other SAML tools accept it.

[jalan]

My mistake, it wasn't Azure sending these odd timestamps, but some other unknown IDP. In any case, many other SAML tools accept an arbitrary number of decimal digits, it seems.

[charleslavon]

@pitbulk what are your thoughts on this issue and the corresponding PR?