Improve display of PrimitiveIds

[GerdP]

I try to fix #10783. I want to show a popup dialog with the list of objects which were not found on the server. We already have a solution for this problem in class DownloadPrimitivesWithReferrersTask. Try for example to download objects "w2,n3,r123456789"
(w2 was redacted, n3 was deleted, r123456789 doesn't yet exist)
I could reuse this dialog after changing DownloadPrimitivesWithReferrersTask.reportProblemDialog() to public but I don't like the way how ids are reported.
Instead of "relation 123456789, way 2" I'd prefer "w2,r123456789" or "w2, r123456789".
This is the input format used in
Order probably doesn't matter, at the moment it is random because unordered collections are used to store the ids.