Feat: Implement database entry counting

CityDoctorParent/CityDoctorModel/src/main/java/de/hft/stuttgart/citydoctor2/database/DatabaseHandler.java

@@ -148,6 +148,23 @@ public class DatabaseHandler {
         return intersectingObjects;
     }
 
+    public static int getFeatureCount() {
+        int count = -1;
+
+        try (Connection con = new ConnectionWrapper(H2GISDBFactory.openSpatialDataBase(DB_NAME))) {
+            try (PreparedStatement ps = con.prepareStatement("SELECT COUNT(gmlid) AS nr FROM features")) {
+                ResultSet rs = ps.executeQuery();
+                if (rs.next()) {
+                    count = rs.getInt("nr");
+                }
+            }
+        } catch (SQLException e) {
+            logger.error("Connection to database failed while trying to get bbox intersecting objects!");
+            logger.debug(e.getMessage());
+        }
+        return count;
+    }
+
     private static List<? extends CityObject> retrieveCityObjects(ResultSet rs) throws SQLException {
         List<CityObject> cos = new ArrayList<>();
         while (rs.next()) {