Partial class should be code generated as abstract

[Matthias Schoettle]

When generating code for a class that is partial, it should be generated as abstract.

I.e., like a partial class that needs to be mapped, an abstract class needs to be specialized in order to be used.

[Matthias Schoettle]

Resolves #455: Adds abstract class generation for partial classes.

→ <<cset 0df64d75c34b>>