Show "suggested shelf locations" in main panel

[danmichaelo]

When used as a helping tool for reference questions at the counter, the goal might not be one or more specific books, but rather one or more shelf locations where the user can continue to browse for themselves. But identifying the most relevant shelf locations is not straightforward in a long list of books. Currently, you have to open a few items in Primo and check their shelf location there, but you don't really get an overviw of which shelf locations are most used.

We could probably support this better by showing the most common call codes (whether Dewey, MSC or some other system) used with the currently selected subject. This probably only makes sense when some location filter has been set (library or location).

Suggested by Shelly, but I immediately recognized the need for this from my own experience.