Notification: re-notify only when status changes

[dllud]

Current behaviour: AIMSICD issues at least two notifications every time the phone changes base stations ("detecting" followed by "status ok/bad").

Problem: People using a screen-reader (TTS) to read their notifications (visually impaired, professional drivers, etc.) are constantly annoyed by AIMSICD, to the point they are forced to either turn off the screen-reader or uninstall AIMSICD. Even when walking down the street the frequency of notifications is annoying, when driving it is simply unbearable.

Correct behaviour: drop the "detecting" notification and only issue a new "status" notification if status actually changes (e.g., from "ok" to "bad").