Initial KnpMenuBundle integration

> Story: [EZP-22601](https://jira.ez.no/browse/EZP-22601)
> Status: WIP

Integrates a totally non-configurable two level navigation menu, similar to that of ezdemo, to the DemoBundle. Clearly needs to be rewritten,  but it has the basics.

![knpmenu1 pnhg](https://cloud.githubusercontent.com/assets/235928/3598609/77b60f90-0ce5-11e4-97cb-737f384f6c3f.PNG)

Sounds good, I'll integrate that. Should go with a documentation page.