Removed signal handlers from draw3

+ caused deadlocks on program exit, as functions called from signal handler were not async-signal-safe (see: man signal-safety). Amongst others, malloc and pthread_join are not safe.
+ OS will cleanup our threads and db queue anyway
+ saving defined user params on exit is no longer necessary as we save them on every edit action
+ because of all the above, we can safely leave signal handling and cleanup to standard OS behavior on Linux