Add support to OATH OCRA

[robotiko]

The latest update from OATH includes a new challenge-response schema as part of the OTP tools.
Specifications can be found http://tools.ietf.org/html/rfc6287 (http://www.openauthentication.org/specifications) . It should be included to support all the OATH Authentication Methods in the module.

[guyht]

Robotiko has contacted me personally about this and I think it would be really great addition to NOTP so if anyone is willing to take on the work, I would be very happy to mege/publish it.

G