UI: Make it more obvious that the table is x-scrollable

[fhennig]

This is a screenshot of the search table:

There are a few more columns to the right, but it isn't clear from the UI.

[theosanderson]

I also created an issue for this (#3387) but good to have yours to make it clearer what the issue is. I have a clear idea of how we can fix this - using the browser window's scrollbar - and made a partial demo in #3386 but it might be a fair bit of work to get it fully working

[theosanderson]

(I guess we could also use some other approach where we make a fake scrollbar)