added toolbartemplate for homepage

__Tasks:__

- [x] add toolbar template for homepage
- [x] change fallback for callbacks for toolbar to use default if none found
- [x] add abstraction for user object
- [x] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| Tests pass?   | none
| Fixed tickets | none
| Doc           | none