Added missing security checks

Added the missing security checks for controller and navigation items in admin to Categories, Tags and Snippets.

__Tasks:__

- [ ] test coverage
- [ ] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | fixes #467 
| BC Breaks     | Security have to be set correctly, otherwise users won't be able to work on categories, tags and snippets
| Doc           | none