HTML representation for Jupyter notebooks

[gtca]

Jupyter notebooks allow objects to have rich representationhttps://ipython.readthedocs.io/en/stable/config/integrating.html by implementing a spacial formatter, e.g. _repr_html_() for HTML.

This is something that xarray uses to display rich and interactive object representation. Having this feature will enhance user experience with MuData objects when working in Jupyter notebooks and similar environments.

To switch between 'text' and 'html' representations, global options for muon might need to be introduced, e.g. mu.set_options(display_style='html').