Remove duplicate recording labels

If a release has more than one catalog number on the same recording
label then the label name is duplicated as it appears with each
catalog number. As we're not using the catalog numbers skip adding the
recording label to the list if it's already present.

For an example album see
https://musicbrainz.org/ws/2/release/082bc530-580c-4628-8aa9-9003118ffa8b?inc=labels
Don't duplicate penultimate label in multiple album dialog

The penultimate label was used a second time instead of the final
label if there was more than one label.
Use a single cell renderer in the multiple album dialog

Using separate renderers for each line of the release details leads to
extra space between the lines. Use a single renderer with multiple
lines to get better line spacing.
Increase the height of the multiple album dialog

It wasn't big enough to show two albums at once.