Allow ewoks widgets to be connected to orange widgets

Currently the type of the Inputs and Outputs of a widget is Variable.

Find a way to keep the orange way of defining inputs and outputs

    class Inputs:
        xas_obj = Input("xas_obj", XASObject, default=True)
        # simple compatibility for some Orange widget and especialy the
        # 'spectroscopy add-on'
        data_table = Input("Data", Orange.data.Table)

but pass then as Variable between ewoks tasks because of the hashing.