Resolve "Add equals/hash methods for serializable classes"

Closes #54 (closed)

uc4-application/src/main/java/theodolite/uc4/streamprocessing/HourOfDayKey.java

 package theodolite.uc4.streamprocessing;
 
+import java.util.Objects;
+
 /**
  * Composed key of an hour of the day and a sensor id.
  */
@@ -26,4 +28,22 @@ public class HourOfDayKey {
     return this.sensorId + ";" + this.hourOfDay;
   }
 
+  @Override
+  public int hashCode() {
+    return Objects.hash(this.hourOfDay, this.sensorId);
+  }
+
+  @Override
+  public boolean equals(final Object obj) {
+    if (obj == this) {
+      return true;
+    }
+    if (obj instanceof HourOfDayKey) {
+      final HourOfDayKey other = (HourOfDayKey) obj;
+      return Objects.equals(this.hourOfDay, other.hourOfDay)
+          && Objects.equals(this.sensorId, other.sensorId);
+    }
+    return false;
+  }
+
 }