Make sure the Cql Demo solution only uses publicly visible members

[ewoutkramer]

In our work on 2.0, we might have misused the fact that the Demo libraries are friends to the CQL libraries, so they can use internal stuff. Remove that friendship and make sure everything needed for the Demo is public.

We might decide at this point to no longer support calling the Lambdas (Linq.Expression) directly, since we'd like to ditch that in a future version anyway.