Handle signals correctly on linux

Basically do not call nonreentrant functions from a signal handler. In fact, don't use a signal handler at all! This means cores finally get dumped.

Only under linux. Mac and Windows stay the same because I don't care.

"Signal caught" and "signal_handler() error" have also been renamed to "Process killed by signal".

In GUI:

In log:

Process killed by signal: SIGSEGV - segment violation (core dumped)

Shutdown tty console