Better handle existing perms in add_default_permissions
Enhance units code for dealing with polygons and area

Allow specifying default units for plugins
Add square meters and square feet
Allow specifying a storage unit which is separate from the default display unit
Show area in edits page for polygon fields

Also move all audits display logic for geometry fields into audit.py
Show unit name abbreviations in Edits page
Show all mapfeatures on the edits page
Clean up recent_user_edits template
Clean up unit conversion dict
Merge pull request #1132 from maurizi/topic/mapfeature-edits

Show all mapfeature edits