Add paper_trail to Mapping
Record history of Mapping using paper_trail
Remove odd usage of polymorphic_path
Put the history to the right of the edit form

(it'll pop underneath the Save button in narrower viewports)
Provide version summary for mappings

Integrates paper_trail
Shows mapping changes at summary level (who, when, not what yet)
Show what was changed in the version page
Don't link the events when showing detailed versions

Also, anchor the versions so they can be highlighted later.
Highlight the changeset indicated in the fragid
Add breadcrumb to Versions#index
Merge remote-tracking branch 'origin/paper-trail'