Solar System demo app

Solar System sim assignment from Coursera / MSU game design class. 

Modifications:

- Added all planets (and Pluto)

- Added movable camera with WASD / mouse. Can fly around in space, zoom in zoom out.

- Left Clicking on object will enter orbit around it, right click will focus on Sun.  Also comets are clickable! 

- Added Label to show which planet is the focus

By Bryan Starbuck