Delete all displaysets warning is unclear

[miriam-groeneveld]

Describe the bug A clear and concise description of what the bug is.

To Reproduce Steps to reproduce the behavior:

1. Go to a reader study where all cases are answered
2. Click on Cases
3. Click on Delete all displaysets
4. The text No editable display sets selected. is displayed. This does not tell the user what they should do to delete all display sets.

Expected behavior The text should tell the user what should be done (first delete all answers).

Screenshots If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context Add any other context about the problem here.