Use 'Acl.' as plugin prefix and pluralized class name in ACL behavior

[nook24]

• The AclBehavior used the singular table name to add the hasMany association which leats to usage of the wrong table.

• I also replaced App::className() with Acl. because the Acl Plugin was using generic auto generated Cake\ORM\Table instead of Acl\Model\Table\ I checked some other CakePHP plugins and none of it was using App::className()