Add "liveClicker" use-case and possibility to lock live feedback

Live Clicker

An additional use-case called "liveClicker" has been added (https://scm.thm.de/redmine/issues/17162). It uses the live feedback implementation in order to make the voting in the style of hardware clicker systems possible. The timed deletion of feedback votes has been disabled for sessions with "liveClicker" configuration.

Feedback lock

The feedback-lock feature allows the speaker to lock the live feedback/clicker. While the lock is active, no further votes are possible. On lock removal all votes from the session will be reseted.