LOTS of changes to properly handle post/topic revisions

FIX: history revision can now properly be hidden
FIX: PostRevision serializer is now entirely dynamic to properly handle
hidden revisions
FIX: default history modal to "side by side" view on mobile
FIX: properly hiden which revision has been hidden
UX: inline category/user/wiki/post_type changes with the revision
details
FEATURE: new '/posts/:post_id/revisions/latest' endpoint to retrieve
latest revision
UX: do not show the hide/show revision button on mobile (no room for
them)
UX: remove CSS transitions on the buttons in the history modal
FIX: PostRevisor now handles all the changes that might create new
revisions
FIX: PostRevision.ensure_consistency! was wrong due to off by 1
mistake...
refactored topic's callbacks for better readability
extracted 'PostRevisionGuardian'

spec/models/draft_spec.rb

@@ -73,7 +73,7 @@ describe Draft do
     it 'nukes the post draft when a post is revised' do
       p = Fabricate(:post)
       Draft.set(p.user, p.topic.draft_key, 0,'hello')
-      p.revise(p.user, 'another test')
+      p.revise(p.user, { raw: 'another test' })
       s = DraftSequence.current(p.user, p.topic.draft_key)
       Draft.get(p.user, p.topic.draft_key, s).should == nil
     end