Fixed tag_cloud helper to actually generate the correct css tags

Changed the count method to taggings_count, which looks to be a true property on the ActsAsTaggableOn::Tag object, and fixes the tag_cloud helper.
add back the taggables index in the taggings table
Merge pull request #555 from TheLarkInn/master

Fixed tag_cloud helper to actually generate the correct css tags
Merge pull request #556 from pcai/master

add back the taggables index in the taggings table