Option to reload UI when assets are updated

Closes #62

When the boolean is set to true, the UI reloads after the update command finishes. It looks best when `FlxG.autoPause` is false.

Here I moved the button around and changed the value of the parameter that gets traced when the button is clicked.
![image](https://cloud.githubusercontent.com/assets/5033927/3263721/6018b1e2-f275-11e3-95ef-45419bbe456c.png)