+ 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

+ there is a lock introduced in "Add global parser synchronous access mutex", but still draw3 segfaults on init
+ segfaults are not reproducible using valgrind, and happen in AddPar, where curr points to a badly initialized structure
+ altogether this looks very much like a multithreading issue
+ so introduce a recursive_lock, locking every single function in libparnt
+ this is extremely ugly, but it works and it doesn't slow down program start remarkably
+ a proper fix would be removing all the libparnt code and writing a new, simple, parser for szarp.cfg