Sir sigurd patch 1 (#1192)
Sir sigurd patch 1 (#1192)

* Inherit Folder from MPTTModel instead of using mptt.register().

The preferred way to do model registration is via model inheritance and `mptt.AlreadyRegistered` is deprecated since django-mptt 0.4

https://django-mptt.readthedocs.io/en/latest/upgrade.html?highlight=mptt.register#use-model-inheritance-where-possible

* changed module import

* add message for #1068

Co-authored-by: Sergey Fedoseev <12ccfc34a576e22353a02ccc41f1e07a8efa0bc3@gmail.com>
divio/django-filer,divio/django-filer,webu/django-filer,webu/django-filer,webu/django-filer,divio/django-filer,webu/django-filer,divio/django-filer