disposable UI; loading screen mockup (i heard like loading screen -- sonic 06)

src/net/torvald/terrarum/ui/UIItemImageGallery.kt

@@ -69,4 +69,8 @@ class UIItemImageGallery(
     override fun scrolled(amount: Int): Boolean {
         TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
     }
+
+    override fun dispose() {
+        imageList.forEach { it.dispose() }
+    }
 }