There is an situation when images with the same name-version but
different release are in the completely different repositories.
For example, foo-1-1 is built against fedora-28, foo-1-2 is built
against fedora-29.

Current Freshmaker deduplication code replaces foo-1-1 with foo-1-2,
because the Release is higher, but this is wrong, because both images
live in different container repositories and are "unrelated".

This commit fixes this by grouping images not only by name-version,
but also by the sorted list of the repositories the images are in.

Thanks to that, foo-1-1 won't be treated as older release of foo-1-2,
because they repositories do not match.