[HOTFIX] Fixed a block issues

* Remove and Add button visibility
* Type dropdown (content and visibility)
* No sortable if only one block exists
* Smart-content headline

__Tasks:__

- [ ] test coverage
- [ ] gather feedback for my changes
- [ ] submit changes to the documentation

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | none
| BC Breaks     | none
| Doc           | none