[FEATURE] Restructured content for Twig template

Changed templates due to new structure, depends on https://github.com/sulu-cmf/SuluContentBundle/pull/211, https://github.com/sulu-cmf/SuluWebsiteBundle/pull/41, https://github.com/sulu-cmf/sulu/pull/225 and https://github.com/sulu-cmf/SuluMediaBundle/pull/69

__Tasks:__

- [x] test coverage
- [ ] gather feedback for my changes
- [x] submit changes to the documentation

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | none
| BC Breaks     | Changed variables available in twig templates
| Doc           | https://github.com/sulu-cmf/docs/blob/master/developer-documentation/300-webspaces/templates.md