py-django-filer: updated to 1.6.0

1.6.0:
Removed support for Django <= 1.10
Removed outdated files
Code alignments with other addons
Replace deprecated templatetag staticfiles against static.
Added management command filer_check to check the integrity of the database against the file system, and vice versa.
Add jQuery as AdminFileWidget Media dependency
Add rel="noopener noreferrer" for tab nabbing
Fixed an issue where a value error is raised when no folder is selected
Fixed search field overflow

1.5.0:
Added support for Django 2.2
Adapted test matrix
Adapted test structure and added fixes

(adam)