EZP-21018: updated REST API to use proper symfony route arguments + url generation

http://jira.ez.no/browse/EZP-21018.

Updates to `EzPublishRestBundle` / `eZPublish/Core/REST`:
- The router is used to provide controllers with arguments
- The router is used to generate urls.

The existing urlHandler is still present as other elements depend on it (ValueObjectVisitors for instance). This will be covered in a further PR.