Users who attempt to create courses without access rights should get an error message

[regisb]

Unprivileged users who attempt to create a course fail to do so (rightly) and no error message is displayed (and that is the actual issue).

How to reproduce:

1. Sign up/login as unprivileged user
2. Go to the studio and attempt to create a course
3. Click "Create": nothing happens.

In the background, a POST http:///course request is made, with a 403 response. But that error is not caught in the frontend and no error message is displayed.

Instead, there should be an error message that basically says "You are not allowed to create a new course within this organization".

This issue was described here: https://discuss.openedx.org/t/sandbox-studio-does-not-create-course/14010/6
Here's a screencast that highlights the issue: https://drive.google.com/file/d/1hUQfxV4BvPZy8kwhF10ITpXTm91yLze1/view?usp=sharing

[KristinAoki]

@regisb there PR #1079 in progress to add more error messages when trying to render pages. Will you leave a comment there so that the author can make sure this case is included.

[arbrandes]

The fix was merged to master.