use anti_spam plugin in suggest_articles

ActionItem2691
Merge remote-tracking branch 'lucasmelo/spam' into lucas-spam
anti_spam_plugin: refactor wrappers logic
spammable: encapsulate the spam logic to a module
spammable_hot_spot: encapsulating spammable hot_spots
spammable: fail safe measures

   * Avoiding module inclusion on models that doesn't have a spam
     attribute.
   * Avoiding named_scope filters on models that doesn't have
     named_scope.
manage-spam: show only tabs that has spam
schema: remove mistakenly added plugins tables