Resolve "Select module of newly created assignment after assignment is created"

Summary

When creating a new module for a course edition, the page we return to is the one we were previously viewing before starting the creation process. Intuitively, the user would expect to see the newly created module instead.

Checklist

All items on this checklist should be checked.

• I have added a changelog entry.
• I have added a test that catches the original bug behaviour.
• I adhere to the style guide.

How to review

1. Log in as somebody allowed to create new modules for an already existing course edition
2. Go to the course edition where you want to add the module
3. Create a module
4. The previously created module should be selected in the dropdown.
5. The previously created module should be displayed in the widget below.
6. The previously created module should appear on the remove button.
7. All 3 previous points should display the first module in the list if no new modules were added.

Closes #725