Added support for "lock" and "unlock" commands which will just lock (or unlock)

the list database (sbbslist.json) for external processing/modification. When
run via jsexec (as intended), jsexec will return 0 if the lock/unlock operation
was successful, -1 otherwise. It would be wise to check the errorlevel/return
value of jsexec for successful lock before operating on the list file.