New signals and slots syntax to support interface classes

The new signals and slots syntax cannot be used with the interface classes, which don't have Q_OBJECT defined. The compilation fails on missing Q_OBJECT when the signal is defined in the interface class and there is no way to define the signal in the implementing class and use it via the interface in the new syntax. This is feasible with the old syntax.

It would be great if this can be implemented into the new signals and slots syntax.