Diff - String comparison lengths

Instead of comparing each word (which can get confusing if you have many words that have changed), compare each line, that's at most 80 characters.
Merge pull request #110 from Moustacha/diff-line

Diff - String comparison lengths
Merge pull request #109 from Moustacha/setup-manifest

Setup & manifest
Keep Moderation History

Add an option to GenericModerator that controls whether history of
 moderated objects should be kept or not.

Add a new "date_updated" field to ModeratedObject so that we can
 determine what the latest object is.

Update ModerationObjectManager.get_for_instance to try and get the
 moderated object the old way,.and if there are too many (because keep_history = True),
 find the most recent one and return that.

Add a test to make sure the post save handler works with keep_history

Add a test for ModeratedObjectManager to test get_for_instance