Test abstract decorators functionally

The current assertions for abstract decorators are just testing that abstract classes annotated with decorators can be enabled and are resolved correctly. However, no functionality test involving abstract decorators is carried out.

The assertions should test that:

a) abstract decorators can be applied at all (i.e. instantiated)
b) methods which are not decorating methods of the decorated type cannot be abstract (DefinitionException)
c) when abstract decorating method are called as part of the decorator chain, they are actually deferring the call to the injected delegate