added support for cross-assembly discriminator properties

[markusbuschhoff]

... that use fully qualified names

This simple patch allows for using JsonSubTypes with fully qualified or assembly qualified names to access cross-assembly subtypes via discriminator properties.

This also allows to use fully qualified names at all - beforhand they could not be found even if in same assembly.

Example baseclass usage that now can be derived in another assembly:

[JsonConverter(typeof(JsonSubtypes), "JSONType")]
public class MyBaseClass
{
    public string JSONType { get { return this.GetType().AssemblyQualifiedName; } }
}

[manuc66]

Hi @markusbuschhoff

Could you add another assembly to the solution and a new test case ?

Thanks !