Stop button should stop the current command

[buha]

Currently, the Stop button stops the sequence execution right after the completion of the ongoing command. However, if the prober doesn't send an SRQ when the user awaits it and if large timeouts (tens of seconds) are used, the GUI is locked.

Perhaps command execution threads may be killed without consequences. It is definitely not good practice but neither is it better trying to bypass the use of hardware timers (the root cause).