Missed call rework: Use dbus to check for missed calls & properly delete pickup

Use dbus to monitor for missed calls. Missed calls used to work but had a
regression due to the work to make text/calls used dbus. This adds the proper
dbus hook for missed calls as well and also changes the incoming call
notification to allow for multiple incoming calls (theoretically).

Tested for a single caller and transitioning the pickup notification
into a missed call notification and all is working good.

scripts/modem/sxmo_modemmonitortoggle.sh

@@ -5,7 +5,8 @@ else
 	sxmo_modemmonitor.sh &
 fi
 
-rm /tmp/sxmo_incomingcall
+NOTIFDIR="$XDG_CONFIG_HOME"/sxmo/notifications
+rm $NOTIFDIR/incomingcall*
 
 # E.g. wait until process killed or started -- maybe there's a better way..
 sleep 1