Add plugin hook on `GaleryViewThumbnail`.

[AdrienDerobert]

There is a little inconsistency with thumbnail components. The IIIFThumbnail is used in the GalleryViewThumbnail and ThumbnailCanvasGrouping. But only IIIFThumbnail and ThumbnailCanvasGrouping have the withPlugin hook.

This makes the wrap plugins only able to target either:

• galery and navigation.
• navigation only.

The gallery only behavior is impossible to do today.

Proposed fix: add the with plugin hook to GalleryViewThumbnail.