Today I have finished a new sample implementation of permission UI. Here is the screenshot 
New permissions UI
The (x) allows quick removing of permission or prohibits, the (+) leads to a form where you can select role to be given permission or marked as prohibited.
Is this easier to understand and use for ordinary teachers?
Hi Petr
Is there a tracker issue fir this?
There is no specific tracker issue yet, because i is part of much larger patch. I am working on a proposal which will be published in our docs wiki soon.