Add a new signal handler for SIGQUIT
Add a new signal handler for SIGQUIT. SIGQUIT signals the session service to stop ALL sessions.
Works with and without mockup mode.
How to send SIGQUIT via a terminal emulator:
stty -a | grep intr
(for me it's CTRL+\ (CTRL+ALTGR+? on german Keyboard))
!5 (merged) is required to be merged for this MR!