fix bug in tags_synonyms_copy_tagged_items management command

now it properly checks for errors in the dry run
also, it will never raise Validation or Integrity errors - it prints them and continues

need to re-run the management command:

dry run:
./manage.py tags_synonyms_copy_tagged_items

if looks ok, run for real:
./manage.py tags_synonyms_copy_tagged_items --no-dry-run