Not possible to make public control list private again

[carinedengler]

Hi, this is not necessarily the most pressing issue, I ran into when working on #149 and add it here to at least document it since I found the behavior a bit unexpected.

Describe the bug
It is possible to make a control list public, but not to make it private again.

To Reproduce
Steps to reproduce the behavior:

1. create new control list
2. go to control list view
3. click on red button to make it public
4. no button to make it private again, apparently no other configuration option

Expected behavior
Either a button to make the control list private again, or a warning (pop-up window?) explaining me that this cannot be undone.