some fixes [multithreading,..]

needed interface changes [new options]
logger for android
wifi-ap-optimization
new test-cases

sensors/radio/WiFiMeasurements.h

@@ -13,6 +13,15 @@ struct WiFiMeasurements {
 	/** all contained measurements */
 	std::vector<WiFiMeasurement> entries;
 
+	/** convert to string */
+	std::string asString() const {
+		std::string res;
+		for (const WiFiMeasurement& m : entries) {
+			res += m.getAP().getMAC().asString() + ": " + std::to_string(m.getRSSI()) + "\n";
+		}
+		return res;
+	}
+
 };
 
 #endif // WIFIMEASUREMENTS_H