Ace input

Fixed my horrendous mistakes in the seed file I put in the gist
Added ACE input area to both new and update, and read only to code_snippet#show and on the tutorial main.
tutorial_path now shows everything in it, with stuff sorted by :order_number
Author can move code blocks up and down to rearrange order (Will do paragraphs on train in morning)
Added gray background to ACE editor for Neal

Question: Do sub_chapters need an order number? So we can sort them?