Model as dict

as per https://github.com/hyperspy/hyperspy/wiki/HSPEP1%3A-Save-models-in-the-same-hdf5-file-as-the-data

Still lacks user guide entries and tests (any ideas for them are welcome, as none similar are present at the moment)



As a "big" data user, I would prefer not a deepcopy in "as_dictionary". I'm often close to my memory limit and I don't want to crash my computer when saving. Slicing in the rest of hyperspy deepcopy, isn't it? My preference is to keep it the way hyperspy works.