BAC-821 add isBlockedCheck in SpecialAchievementsCustomize, and add PreventBlockedUsers trait (used by WikiaController) which can prevent a user from accessing/editing content if they're blocked.

this functionality is opt-in, and currently only used by WikiFeaturesSpecialController (Special:WikiFeatures)
formatting some code to wikia standards
updating static vars to make more sense
extending PreventBlockedUsers trait with PreventBlockedUsersThrowsError so classes that use these don't need to specify the action, removing vars from PreventBlockedUsers, and removing "use PreventBlockedUsers;" from base WikiaController
Merge remote-tracking branch 'origin/dev' into BAC-821
fixed/added some documentation
Merge pull request #1586 from Wikia/BAC-821

BAC-821 - prevent blocked users from taking action