BAC-821 - prevent blocked users from taking action

https://wikia-inc.atlassian.net/browse/BAC-821

Added trait PreventBlockedUsers that encapsulates the logic to prevent users from accessing restricted content. Used by WikiaController, and opted-in for WikiaFeaturesSpecialController (as this was called out in the JIRA). 

Also added an isBlocked() check for SpecialAchievementsCustomize (also called out in the JIRA)