(WIP) Enhance signal handling

[michaelortmann]

Found by: michaelortmann Patch by: michaelortmann Fixes:

One-line summary:

Additional description (if needed):

Test cases demonstrating functionality (if applicable): Hammering the bot with signals could trigger a race and lead to crash, like:

[11:37:45] Received QUIT signal: restarting...
[11:37:45] Received QUIT signal: restarting...
[11:37:45] Received QUIT signal: restarting...

Aborted (core dumped)