Configuration file backup level (count) should be configurable

As it is now, controlling config file backups requires using the SCFG -b option and there's now control over SBBSCTRL's used backup level. If we make this a configuration options (e.g. SCFG->System->Advanced->Config File Backups), then it could be used both in SCFG and SBBSCTRL, command-line options needed.