Add LocationEdit table to track edits to Location objects

This object tracks the new value, edit type, user who edited
the Location, review status, and the Location.
Add accepted field to Location model/object

This field tracks whether or not a location has been added
and reviewed. New locations added by non-admins need to be
reviewed before they are available in the application. This
field tracks that status.
Modify existing queries for Locations to only return
those that have been reviewed by adn admin.
Add helper method that returns a list of boolean
fieldnames
Set optional class on map widget if class attribute passed
Add filter to browse locations by pending edits
Override __init__ of LocationForm to highlight edited fields

When loading a change form this looks at pending edits and
applies the appropriate class to the field based on whether
an edit is present and if what type of edit it was.

- updates = yellow
- create = green
- delete = red
Move all general settings to top of LocationAdmin class
Subclass Django Admin to allow for edits/approval

Changes present
- add helper method to delete messages in a request
- override changelist_view to only display some filters
to non-admins
- add custom 'reject_updates' url/view to allow for bulk
rejecting of edits
- override 'render_change_form' to allow custom messages
when displaying form
- override 'response_add' to change message when non-admin
submits new location
- override 'save_model' to take appropriate action based
on user privileges and edit type
- override 'delete_model' and 'view' to display appropriate
message and take correct action
Override change_form and buttons to reflect admin approval
Change delete confirmation page language, make edits as per John
Add helper function to check if user has edit approval privileges
Replace superuser requirement with approve_edit group requirement

As per Kenny's comment the superuser requirement is removed.

Now, in the admin the superuser must create a group called
'approve_edit' that has privileges for editing the location
object (add, change, delete, etc.).
Merge pull request #357 from notthatbreezy/topic/admin-approve-edits

Topic/admin approve edits