Make VariantReporting Reporters into SoftwareResults

There is some odd indirection/inefficiency here because calling `unique_results` already joins through `users`. It seems like we shouldn't iterate through them a second time to do the filtering. Perhaps `unique_results` should take a label? Alternately something like `uniq map { $_->result } $self->result_users(label => $label)` would work without iterating the users redundantly.