Add call number(s) to multi-lib copy summary

Add call number(s) to multi-lib copy summary

For a copy summary showing available copies at more than one library, we now
display the list of call numbers at that library (but only those call numbers
with available copies)

Where previously we displayed:
7 available at Example Branch 1
7 available at Example Branch 2

Now we display:
7 available at Example Branch 1 call numbers CONCERTO 699, PERFORM 699
7 available at Example Branch 2 call numbers CONCERTO 699, PERFORM 699

Signed-off-by: Jeff Godin <jgodin@tadl.org>