fix way to get DataPoint

src/main/java/ch/hevs/isi/core/BooleanDataPoint.java

@@ -25,7 +25,7 @@ public class BooleanDataPoint extends DataPoint{
     public String toString(){
         String s;
         s = this.getLabel();
-        s += ": ";
+        s += "=";
         s += this.getValue();
         return s;
     }

src/main/java/ch/hevs/isi/core/FloatDataPoint.java

@@ -25,7 +25,7 @@ public class FloatDataPoint extends DataPoint{
     public String toString(){
         String s;
         s = this.getLabel();
-        s += ": ";
+        s += "=";
         s += this.getValue();
         return s;
     }