Generalize merge_histories to work for other models
Fix template to correctly show photo edits

The template will now show photo edits as well as entry edits.
It will leave the table fields blank that don't apply to the photo
edits, like species and dbh class.
Add photo edits to recent_edits summary page
Sort recent edits summary page by most recent
Merge pull request #142 from steventlamb/bug/show_photo_edits

Bug/show photo edits