Log Message:
py-djangocms-file: updated to 2.4.0

2.4.0:
Added support for Django 3.0
Added further tests to raise coverage
Fixed smaller issues found during testing

2.3.0:
Added support for Django 2.2 and django CMS 3.7
Removed support for Django 2.0
Extended test matrix
Added isort and adapted imports
Adapted code base to align with other supported addons