refs. https://github.com/TryGhost/Product/issues/3349
It's a bit cumbersome how design and theme navigation is handled in
AdminX at the moment. On a high level, this PR applies the following
changes:
- Change theme is under Design settings
- After activating a theme, Design settings are automatically opened
refs https://github.com/TryGhost/Team/issues/3349
Tidies up the remaining major pieces which were not covered by tests.
Extends the existing test patterns, although the API mocks are getting a
bit unmanageable.
