Multiple super-categories - layout fixes

[will-moore]

IDR only uses 2 super categories - Tissue and Cell.
But support for more (fix the layout) would be useful for other users.
See https://forum.image.sc/t/omero-gallery-lock-up-issue-and-different-viewer-option/34259/6

[will-moore]

I think that allowing categories to be shown with only an orange button (as on http://idr.openmicroscopy.org/about/) instead of with an Image, would allow more super-categories to be shown.

As discussed with IDR team: config should allow display of super-categories with OR without an image.