gui: allow hdf5 to use the metadata widget

The "metadata" widget is cleary oriented edf-spec and even fabio as it uses the fabio 'kind' concept. It was ignored for HDF5 from !253 (merged) This PR allow HDF5 metadata to be displayed by this interface. But with very strong limitation. The 'kind' (positioner, default, counter) will be simply ignored and the table will always display all the 1D dataset available from the HDF5 metadada group like:

or for another kind (same output as expected)