added stackable functionality to items and improved inventory management

src/de/miaurizius/jgame2d/entity/obstacle/ChestObj.java

@@ -42,13 +42,12 @@ public class ChestObj extends Entity {
         panel.playSE(3);
         StringBuilder sb = new StringBuilder();
         sb.append("You open the chest and find a ").append(loot.name).append("!");
-        if(panel.player.inventory.size() == panel.player.maxInvSize) {
+        if(!panel.player.canObtainItem(loot)) {
             sb.append("\nBut your inventory is full...");
             panel.ui.currentDialogue = sb.toString();
             return;
         }
         sb.append("\nYou obtain the ").append(loot.name).append("!");
-        panel.player.inventory.add(loot);
         down1 = image2;
         opened = true;
         panel.ui.currentDialogue = sb.toString();