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
Move bulk add mappings filters into a module

* Previously, we had to duplicate the same filters across controllers
* Since we're already including the module, make that include happen
  via a method call instead
* That method call passes through the options to before_filter
* Since the use of the filter also depends on find_site, move that
  into the module too
Be consistent in language with other mixins

* acts_as_taggable_on
* has_paper_trail
* tracks_mappings_progress (not the imperative track_mappings_progress)