Add OAuth validator Guice provider to allow injection to auth handler

Currently the code in OAuthAuthenticationHandler create OAuth validator for each validate call.

This change add validator as injection variable to the authentication handler.
This will allow extension for custom OAuthValidator impl.

[henry.saputra, 2011-04-27 07:33:57]

Move OAuthValidator as injection variable for OAuthAuthenticationHandler.

This will make extension and code reuse easier  to provide custom impl for
OAuthValidator for OAuth.

- Henry