adapted class PlantListModel to PlantDatabase

#12

src/main/java/ch/zhaw/gartenverwaltung/io/JsonPlantDatabase.java

@@ -56,9 +56,9 @@ public class JsonPlantDatabase implements PlantDatabase {
      * @see PlantDatabase#getPlantById(long)
      */
     @Override
-    public Optional<Plant> getPlantById(long id) throws HardinessZoneNotSetException, IOException {
+    public Optional<Plant> getPlantById(HardinessZone zone, long id) throws HardinessZoneNotSetException, IOException {
         if (plantMap.isEmpty()) {
-            loadPlantList(currentZone);
+            loadPlantList(zone);
         }
         return Optional.ofNullable(plantMap.get(id));
     }

src/main/java/ch/zhaw/gartenverwaltung/io/PlantDatabase.java

@@ -30,5 +30,5 @@ public interface PlantDatabase {
      * @throws IOException If the database cannot be accessed
      * @throws HardinessZoneNotSetException If no {@link HardinessZone} was specified
      */
-    Optional<Plant> getPlantById(long id) throws IOException, HardinessZoneNotSetException;
+    Optional<Plant> getPlantById(HardinessZone zone, long id) throws IOException, HardinessZoneNotSetException;
 }