[feature request] Add _repr_html_() for visualistion in Jupyter Notebooks

[balwierz]

Most users will be using GenomicRanges in Jupyter Lab.
It is important to have a _repr_html_ function showing a human-glanceable preview of a GenomicRanges object in a tabular form.

[jkanche]

wondering what advantages this provides compared to a normal print.

[balwierz]

One of the problems is that Jupiter will use __repr__ if _repr_html_ is not available, and __repr__ of a GenomicRanges object with many columns may clutter the screen.