refs https://github.com/TryGhost/Team/issues/451
Start of new post preview prototype.
- adds preview button next to publish button
- opens new combined preview modal with desktop/email/social tabs
- desktop preview shows front-end preview url in iframe
- email preview fetches preview data as per the older email preview modal
- social preview to come later
no issue
Keeps component JS backing files and template files in the same directory which avoids hunting across directories when working with components. Also lets you see all components when looking at one directory, whereas previously template-only or js-only components may not have been obvious without looking at both directories.
- ran [codemod](https://github.com/ember-codemods/ember-component-template-colocation-migrator/) for app-level components
- manually moved in-repo-addon component templates in `lib/koenig-editor`
- removed all explicit `layout` imports as JS/template associations are now made at build-time removing the need for them
- updated `.embercli` to default to new flat component structure
