New posts pass PostsController sorting function at the top

- PostsController orderBy function sorts posts with isNew to the top, otherwise their undefined dates fail to compare
- also catch when `updated_at` is undefined, happens when model is being written with results from the server
- catch objects of type Error in validation engine, helps catching client errors
- join server errors with BR tag in ajax util
- add `emberBuild` task to `grunt test-functional`
- add a test helper, `thenTransitionAndWaitForScreenLoad`, to test transitioning to major parts of the app
- add a test that transitions from Content to the Editor, and back to Content
Merge pull request #3144 from darvelo/sort-new-posts

New posts pass PostsController sorting function at the top