[FEATURE] Implemented Sitemap

__Tasks:__

- [x] test coverage
- [ ] gather feedback for my changes
- [ ] submit changes to the documentation

__Known Bugs:__

* for multiple Portal urls first will be used
* shadow pages (https://github.com/sulu-cmf/SuluWebsiteBundle/issues/40)

__Dependend PRs:__

* https://github.com/sulu-cmf/sulu/pull/229
* https://github.com/sulu-cmf/SuluTestBundle/pull/23

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | no => because https://github.com/sulu-cmf/sulu/pull/229 , https://github.com/sulu-cmf/SuluTestBundle/pull/23
| Fixed tickets | none
| BC Breaks     | none
| Doc           | TODO
You should not catch the general Exception here, and the explanation could be better. It's obvious that you ignore the exception because there is no route node, but why exactly are you doing that?