Implement ContentPresenter, add content fields to Pages form.

Current spec status: 682 examples, 0 failures in 6.52 seconds.
Implement polymorphic contents for Page#new, #create.

Delegate actions now cache request object.

Current spec status: 696 examples, 0 failures in 6.37 seconds.
Render page contents on Page#show.

Current spec status: 698 examples, 0 failures in 6.84 seconds.
Implement polymorphic contents for Page#edit, #update.

Current spec status: 717 examples, 0 failures in 7.1 seconds.
Merge pull request #9 from sleepingkingstudios/feature-contents

Implement polymorphic Contents for Pages.