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".

Ran unit tests.