Added a class to map object ids so they can be called by name

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

lib/features/entities/pushwall_manager.dart

@@ -1,6 +1,7 @@
 import 'dart:math' as math;
 
 import 'package:wolf_dart/classes/matrix.dart';
+import 'package:wolf_dart/features/entities/map_objects.dart';
 
 class Pushwall {
   int x;
@@ -24,8 +25,7 @@ class PushwallManager {
 
     for (int y = 0; y < objectGrid.length; y++) {
       for (int x = 0; x < objectGrid[y].length; x++) {
-        // Map ID 98 in the object grid marks a pushwall!
-        if (objectGrid[y][x] == 98) {
+        if (objectGrid[y][x] == MapObjectId.secretDoor) {
           pushwalls['$x,$y'] = Pushwall(x, y, wallGrid[y][x]);
         }
       }