performance enhancements

memory enhancements
prevent starting sensors more than once
fix for wifi lag issues
map scaling for huge buildings

sensors/android/BarometerSensorAndroid.h

@@ -22,6 +22,8 @@ private:
 		;
 	}
 
+	bool started = false;
+
 public:
 
 	/** singleton access */
@@ -32,6 +34,9 @@ public:
 
 	void start() override {
 
+		if (started) {return;}
+		started = true;
+
 		auto onSensorData = [&] () {
 			BarometerData data(baro.reading()->pressure() / 100.0f);		// convert Pa to hPa
 			informListeners(data);
@@ -43,7 +48,7 @@ public:
 	}
 
 	bool isRunning() const override {
-		return baro.isActive();
+		return started;
 	}
 
 	void stop() override {