Django 2+ provides a new method for definings URLs, `path()`. This is much simpler for basic cases, and makes URL patterns more readable. In addition, the old `url()` method has been renamed to `re_path()`, and a warning is raised when using the old name, so switch to that too. As part of this, I changed the file attachment URLs to actually parse UUIDs using Django's new converter for that. This required making a change in the test `create_file_attachment_base` method to use real UUIDs instead of the string "test-uuid". Testing Done: Ran unit tests.