Add Tab components

Closes #3937
- Add ghost tab components
- Remove extra container div from Application view
- Move right-outlet viewing logic to application level
- Prepare PSM.hbs for tabbing
Revert "update CodeMirror 4.5.0"
Merge pull request #4042 from novaugust/psm2-tabs

Add Tab components
Merge pull request #4071 from TryGhost/revert-4022-master

Revert "update CodeMirror 4.5.0"
Fix ghost-ui reference

fixes #4072
- Correct reference to ghost.min.css
Merge pull request #4076 from halfdan/4072-404page

Fix ghost-ui reference
Naming cleanup

closes #4069
- Rename everything from camelCase to lowercase + dashes
- Remove usage of `server`, `app` and `instance`