rework ui related scripting stuff

data/modules/mainmenu/init.lua

@@ -0,0 +1,16 @@
+require 'entergame'
+
+function initializeApplication()
+  mainMenu = loadUI("ui/mainmenu")
+end
+
+function terminateApplication()
+  App.exit()
+end
+
+-- here is where everything starts
+if not initialized then
+  initializeApplication()
+  App.onClose = terminateApplication
+  initialized = true
+end