#746 Display coverart thumbnails with interiorart parent titles

[Ron Maas]

Currently, when a coverart title is displayed the thumbnails of the coverart images for the parent title and its variants are displayed at the bottom of the title record. Occasionally, a coverart title is a variant of an interiorart title (e.g. interior art was first publication). I'd like to request that thumbnails for the variant coverart titles be displayed on their parent's title page just as they would be if their parent were coverart.