Forgot to re-update this to use Model.get_all_field_names(), because Model._meta.fields excludes M2Ms.
View class shouldn't throw an attribute error if self.exclude_fields isn't set.
Safer way to set fields.  Really, we just want to provide hooks to override ModelForm settings, and this way is cleaner.
Write-In utilities tests
declaring an empty field list should not result in a field-less form in the 99% case.
Bug fix: having a list as a class attribute means that changing its elements in one instance changes them in all.  Copy the lists to instance attributes instead.
Adding category to an empty field list results in a form with only the category field.  So don't add it.
WriteInBaseView tests
parent view class already sets exclude_fields now; should be able to override in subclass if you really really want to
WriteInDefaultView tests