PSC Validation, Showing invalid if saved value is out of range, using default PSC=666

Created by: smarek

Depends on #640 being merged

Re-implemented proposal from @banjaxbanjo in https://github.com/SecUpwN/Android-IMSI-Catcher-Detector/commit/40098a0bd2ea8b3fa8da64e92ebfa7101f02f677