Battle simulation implementation v2

src/main/java/edu/ntnu/ericbi/wargames/army/enums/TerrainType.java

 package edu.ntnu.ericbi.wargames.army.enums;
 
 public enum TerrainType {
-    HILL,
-    PLAINS,
-    FOREST
+    HILL("/gui/media/terrains/hill.png"),
+    PLAINS("/gui/media/terrains/plains.png"),
+    FOREST("/gui/media/terrains/forest.png");
+
+    public final String imgUrl;
+    TerrainType(String imgUrl) {
+        this.imgUrl = imgUrl;
+    }
 }