Update DeveloperConsole.lua

I've added a new category to the developer console which allows you to view the explorer. The GUI was written by Anaminus a few months ago, and I just ported it into here.
The explorer gui is only visible if you are the creator, and only loads up if the creator of the place presses the "Explorer Panel" button.
Here is the explorer panel that Anaminus made if you need any verification:
http://www.roblox.com/Explorer-Panel-item?id=127978953