Python blocks QT and pybind11 conflict

[mormj]

When a block inherits from both the block/sync_block base class and from QWidget, we get the following error:

TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

We also get this error in the grc generated class for QT flowgraphs, which is why those use a has-a relationship instead of an is-a