Replace test wallpaper with Nehe Tutorial Wallpapers

This change replaces the default testing wallpaper (cube on green background) with Walter Reid's submission of live wallpaper versions of the Nehe OpenGL tutorials.

This includes Nehe Lesson 02 and Lesson 08, but Walter had actually provided more. He had hosted them at [androidgametutorials.com](http://androidgametutorials.com), which now seems to be defunct. I had saved them locally before the site went down, and they are hosted [here](http://glwallpaperservice.com/downloads/nehe-wallpapers.zip). If anyone wants to take a crack at adding the other Nehe wallpapers, feel free.