Modified Authorization Grant to accept a GET

The RFC Spec for OAuth 2 specifies that the Authorization Grant endpoint be a HTTP GET.  POST is allowed
to be supported, but GET must be implemented according to the spec.  This change modifies authCodeGrant.js
to look for the appropriate parameters in either the query string or the body, so HTTP GET and HTTP POST
are both supported.

Added tests to test/authCodeGrant.js to test both POST and GET functionality.