Upgrade to paper_trail 3.0.2

This will enable us to fix a bug with recording tag changes.
Don't record non-existent changes to tag_list

We were generating changes for the tag_list when it wasn't changing, we think
this was introduced by the background_bulk_add branch.
Merge pull request #280 from alphagov/dont_record_nonsense_tag_list_changes

Don't record nonsense tag list changes
Don't do DB access in the view: saved_mapping_ids