factor new_post into a reusable class
roll all the new editor stuff into the default config

This allows me to assume the preview I want to use is what's being
served by `rake preview`.
change 'drafts' to 'editor'
technically these are all posts, not just drafts
try to use the root provide by `rake preview` in the live preview
turns out ::Octopress is used as a module in plugins
add the ability to create new posts from the editor
use the correct url in the header