SortableAdmin does not work with SimpleListFilter

When model admin is subclass of SortableAdmin and SimpleListFilter is used FieldError exception is raised.
This is because SimpleListFilter defines `parameter_name` and SortableAdmin tries to filter by this field.

This is done in:
https://github.com/jazzband/django-admin-sortable/blob/master/adminsortable/admin.py#L56

Workaround is to override `get_querystring_filters` in `SortableAdmin` subclass and remove any parameter used in `SimpleListFilter`.

I have added minimal test case for this issue in https://github.com/bmihelac/django-admin-sortable/tree/tmp/issue-264-SimpleListFilter

To reproduce:
1. run django devserver
2. go to http://127.0.0.1:8000/admin/samples/category/
3. select any value from filter