CAS-1286: Extract the OAuth client support in its own module and upgrade to pac4j

I' ve fixed all checkstyle warnings for the ```cas-server-support-pac4j``` module but not for the ```cas-server-support-oauth``` module (which should be totally rewritten based on Spring Security OAuth library).

Tests have been updated also, even if the main way to test both modules is to use the *cas-oauth-demo*, branch CAS-1286 : https://github.com/leleuj/cas-oauth-demo/tree/CAS-1286.
For tests purpose, authentication can be delegated to :
- Facebook (OAuth 2.0 support)
- Twitter (OAuth 1.0 support)
- another CAS server with OAuth wrapper (OAuth 2.0 support with CAS)
- another CAS server (CAS support)
- myopenid.com (OpenID support).