Group search results by diagram

With the submaps becoming more and more used, search functionality can be improved not to overload the left panel, and help to browse the results.

In the left panel, if a project has submaps, search results can be grouped by submap, with an overall number of hits per a collapsed "group item". The "group item" should be expandable. The link to a submap should be available only in the "group item", in both collapsed and expanded form.