#570 - Added Exponent and Modulus members to JWKS Discovery Document

Updated the DiscoveryEndpointController:

- Added e & n members to the JsonWebKeyDto
- Retrieved the exponent and modulus members from the Certificate
- Assigned the e & n members of the webKey

This change brings the JWKS Discovery Document into conformance with [JSON Web Key (JWK) Section 4.2.2](http://self-issued.info/docs/draft-jones-json-web-key-00.html#anchor8) where if the algorithm is RSA, then the Exponent and Modulus must be included