Add demos of all modules (OSOE-178)

[Piedone]

This solution should also serve as a demo of all our modules. Probably the best would be to add a setup recipe that enables configures everything for a demo so you can better see what's in there. Maybe add some information about what you can access from a content item on the homepage.

Basically, do everything under https://github.com/Lombiq/Open-Source-Orchard-Core-Extensions#adding-a-new-extension-or-significant-new-features for those features that yet lack this.