Fix blank playlist badges

This address the "blank" badges in playlists, which occurred when there was either a duplicate badge in the playlist or a badge that no longer existed.  Duplicates will now be displayed and can be deleted, and non-existent badges will no longer appear in the playlist.

This also fixes a crash in the guardian dashboard that occurred if a learner was awaiting guardian approval for a claim code that had been deleted by the issuer.

Addresses #749