fixed some issues

some new helper methods
added listener-support to offline-reader

sensors/radio/setup/WiFiFingerprint.h

@@ -57,6 +57,15 @@ struct WiFiFingerprint {
 
 	}
 
+	/** get all measurements for the given MAC */
+	std::vector<WiFiMeasurement> getAllForMAC(const MACAddress& mac) const {
+		std::vector<WiFiMeasurement> res;
+		for (const WiFiMeasurement& m : measurements.entries) {
+			if (m.getAP().getMAC() == mac) {res.push_back(m);}
+		}
+		return res;
+	}
+
 	/** serialize */
 	void write(std::ostream& out) const {
 		out << "pos: " << pos_m.x << " " << pos_m.y << " " << pos_m.z << "\n";