Extend FacebookRedirectLoginHelper storeState and loadState method

Change $state property visibility to protected in order to use by
getSessionFromRedirect which call loadState method and set $state.
Merge pull request #19 from carlsonorozco/master

Change scope on FacebookRedirectLoginHelper state
Exclude tests credentials from commits
Merge pull request #22 from yguedidi/fix-tests-credentials

Exclude tests credentials from commits