[wip] ember-data post exploration

Ref #2699

- Introduce ember data with the FixtureAdapter to start
- Refactor ghostPaths into it's own helper file; add initializer to put
it in all routes and controllers
- Add apiUrl and adminUrl helper functions to ghostPaths
- Add loadInitializers and refactor most initializers into one combined
- Add Post ember data model
- Refactor generateSlug to use title of post and ghostPaths
- Refactor post controller to not reference model.property everywhere
- Refactor post controller to not pass specific attributes it's saving
(possibly a regression)
- Some playing around with sending the user down to the page and trying
to get signin to work seamlessly, but getting a 403 for some reason (can
probably go in it's own PR)