refactor social security code

Change SocialAuthenticationFilter to extend
AbstractAuthenticationProcessingFilter,
and override unsuccessfulAuthentication to handle redirect exception;
Change SocialAuthenticationRedirectException to extend
AuthenticationException;
Add Connection<?> to SocialAuthenticationToken;
Update unit test;
fix unit test and bugs
fix bug in SocialAuthenticationFilter
Fixed NPE caused when returning null for boolean
Unified new social/security signin with original ProviderSignInController code by reusing ProviderSignInAttempt instead of SignInAttempts.