title: How Avoid re-initializing Activity That Takes a long time to initilize
body: <p>I have an app with two screens, and buttons that switch between them. One screen is mainly a listView, but the other has a game engine in it (AndEngine) and it can take a while for the game engine to init the first time the activity is created. 
  So switching between them can cause big delays when going to a new game Engine. However, if I just use the back button, the previous game engine loads much faster. 
  Is there a way I can specify to crete only one game engine and always bring up that instance of the activity? Right now I am using startIntent() to swap screens. Is there some other way?
  A way that allows me to just have a single instance of each activity and swap between them?</p>