UX enhacements

- Fix layout problems in room list and room view

- Add gavel icon to several views

- Show notification after comment creation depending on whether the session is moderated or not

- Set auto acknowledge after comment creation for lecturers and moderators

- Reorder, recolor and fixing tooltips of comment icons like 'correct', 'favorite' etc.

- Correct text color in export dialog

- Add dialog to confirm the deletion of a question

Closes #377 (closed), #376 (closed) , #374 (closed) , #373 (closed) , #379 (closed) , #368 (closed) , #380 (closed)