Django-admin-sort

- Dysfunctional.

- Fix [\183](https://github.com/jrief/django-admin-sortable2/issues/183):
Use `mark_safe` for reorder `div`.

- Fix: Method `adminsortable2.admin.SortableInlineAdminMixin.get_fields` always return
a list instead of sometimes a tuple.

- [\171](https://github.com/jrief/django-admin-sortable2/issues/171):
Adhere to Content Security Policy best practices by removing inline scripts.
- Adopted to Django-2.0 keeping downwards compatibility until Django-1.9.
- Better explanation what to do in case of sorting inconsistency.

- Fixes [\137](https://github.com/jrief/django-admin-sortable2/issues/137):
Allow standard collapsible tabular inline.

- Fix [\164](https://github.com/jrief/django-admin-sortable2/issues/164):
TypeError when `display_list` in admin contains a callable.
- Fix [\160](https://github.com/jrief/django-admin-sortable2/issues/160):
Updated ordering values not getting saved in `TabluarInlineAdmin` / `StackedInlineAdmin`.