DBHandler private gemacht. Fixed #6.

src/main/java/de/uniluebeck/mi/projmi6/db/DBHandler.java

@@ -156,6 +156,10 @@ public class DBHandler {
             "VALUES (?, ?, ?, ?, ?, ?, ?, ?)";
     private static final String DELETE_STATHIST = "DELETE FROM `stationshistorie` WHERE `StatHistID` =?";
 
+    private DBHandler() {
+
+    }
+
     /**
      * Gibt alle {@link Patient} aus der DB zurueck.
      *