Post editor:

- moves everything non writing related to a separate modal.
- makes the editor the central part of the screen.

The modal still needs some love to look better, but that's a first step towards a "Medium" ish editor the way I see it.

Issue #272
- Makes the pages editor settings in a modal.
- Puts the editor at the center of the page.

Issue #272
Merge pull request #291 from fdv/feature/make-new-publication-options/272

Moves the articles and pages settings into a modal so only the editor is displayed.

Solves issue #272.