Converted everything to work with polymorphism

Added "Grootheid" to act as a parent to all children classes, it allows
the main "Weerstation" to update them all better and with cleaner code.

OutsideTemp.java

@@ -0,0 +1,32 @@
+import java.util.ArrayList;
+
+public class OutsideTemp extends Grootheid{
+    
+    //constructor
+    public OutsideTemp(Measurement measurement1, ArrayList<Measurement> measurement2){
+        updateRecent(measurement1);
+        update24Hour(measurement2);
+    }
+
+    
+    public void updateRecent(Measurement measurement1){
+        setCurrent(measurement1.getOutsideTemp());
+    }
+    public void update24Hour(ArrayList<Measurement> measurement2){
+        
+        ArrayList<Double> list = new ArrayList<Double>();
+        
+        for(Measurement ms : measurement2)
+        {
+            list.add(ms.getOutsideTemp());
+        }
+        
+        calculateMaxMinAvg(list);
+    }
+    
+    public void display(){
+        super.display();
+        GUIboard.writePageToMatrix("Buitentemperatuur", "Gemiddelde: " + getAvg(), "");
+    }
+    
+}