IA: generate sourceResource.title correctly (fixes #7708)

Given IA metadata like the following:
{"title": ["Foo", "bar"], "volume": "1880"}
IAMapper should generate sourceResource.title as such:
{"sourceResource": {"title": ["Foo, 1880", "bar, 1880"]}}
IA: Add YIVO Institute Library (fixes #7735)
Merge pull request #41 from dpla/7708-fix-ia-title-take-2

IA: generate sourceResource.title correctly (fixes #7708)