Clicking "Launch Course Builder" with unsaved changes results in a confusing prompt

[brianhogg]

Reproduction Steps

1. Edit a Course
2. Make an edit to the course content
3. Click "Launch Course Builder" at the top without saving

Expected Behavior

Helpful message saying you need to save changes before launching the course builder

Actual Behavior

Default "you have unsaved changes" prompt. If they click Ok by accident (to navigate away) their changes will not be saved.

This issue has been recreated:

• Locally
• On a staging site
• On a production website
• With only LifterLMS and a default theme

[brianhogg]

There's a gutenberg bug that is blocking this, see closed PR for details: #211