Add audit support to polygon models
Add helper functions for handling polygon histories
Add url/view/template for recent edits admin page
Modify polygon update view to populate audit trail
Update polygon detail to show recent edits
Merge branch 'topic/recent_polygons' into v1.3

Conflicts:
	polygons/models.py
Edit styling on polygon popup for results map
Style polygon view/edit pages, add highlight on polygon popup rows
Merge pull request #137 from azavea/topic/polygon_styling

Polygon UI Styling
This random code was included in the original version.

Seems useless and wasteful. Bringing out the Daleks....
Remove docstrings that don't provide detail
Fix polygon photo upload

Polygon photo upload was producing a crash page because
the user was not set.
Merge pull request #138 from ahinz/topic/fix-dumb

This random code was included in the original version.
Merge pull request #139 from steventlamb/bug/polygon_photo

Bug/polygon photo
Fix fields to properly be non-nullable
Order DBH classes by DBH min
Merge pull request #140 from ahinz/topic/fix-migration

Topic/fix migration
Empty database should ignore this field
Merge branch 'topic/fix-migration' into v1.3