add javascript support for opensocial.invalidateCache()

[panjie . pan]

Reviewers: lryan_google.com,


Please review this at http://codereview.appspot.com/61043

Affected files:
  config/container.js
   
features/src/main/javascript/features/opensocial-jsonrpc/jsonrpccontainer.js
  features/src/main/javascript/features/opensocial-reference/container.js
  features/src/main/javascript/features/opensocial-reference/opensocial.js