Don't bother with otm_code for migrations

Migrations will come with predetermined ITreeRegion codes, which should
be written into the migration as ITreeCodeOverride records.

Doing code searches is a second-best method for producing calculable
ecobenefits for species.

Only one of these methods should be used.
Bail out of migrations if species could conflict
Merge pull request #1619 from steventlamb/topic/fix_migrator_species_duplication

Topic/fix migrator species duplication
Add admin actions to comment moderation

This includes: hiding/unhiding, archiving/unarchiving, and unflagging.
Actions can happen on individual rows, or on multiple rows at once
Add UI tests for comment moderation admin actions