fix: handle label and order by biologic suffix in merge groups

[jsstevenson]

close #299

Two related issues

1. If a normalized drug already has a label, other labels in the group should be added as aliases
2. RxNorm provides records for biosimilars that have a four character suffix but are otherwise the same as the base drug in their name. That base name should be the label of the normalized group, and the drug labeled with that name should be the primary concept ID for the group.

Without this PR, we end up with silly drug pages on dgidb like this: