[WIP] Sitemap generation

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #132 
| License       | MIT
| Doc PR        | symfony/symfony-docs#123https://github.com/symfony-cmf/symfony-cmf-docs/issues/607

Started working on that feature. That would be the task:

- [ ] implement generator for phpcr content
- [ ] create decider for content which should be published
- [x] create controller for the output
- [ ] build dynamic route generation depending on config
- [ ] general configuration and optional activating of the phpcr generator
Not really sure, would like to have the schema of the routes (for showing a nice html view) on the one hand, but the decision if it should be shown depends on content and routes. GetAllRoutes() would give all and i would have the content but i think the content is a lazy loading reference, Right? So ... I think we should manually query to get both at once (possible with PHPCR querybuilder?)