Emergency Button/ Did not understand button

[henrixapp]

During a lecture students struggle to understand certain topics and are to intimidated to ask questions/mind asking something in the forum. Therefore, a Emergency/Didnot understand button is proposed to collect timemarks, where students have problems.

The button should be easily accessible and have some introduction. For lecturers there should be the possibility to see the number of marks per video and quickly access those places in order to prepare extra content or clarify it in the discussion.

It might be worth discussing, whether other students should see the marks or not.

This is a first step towards #221 .