Gui radial bar

Implemented the radial bar we talked about. It should be general enough to serve as the radial progress bar for both health and black hole capacity bar. 

Details:
graphics/hud/RadialBar.cs : Specify an origin, radius, bar thickness, bar color to
create.
During draw, pass in the current and max values.

For those who want to see it in action, checkout the commit that says (debug).
Run the game to see the radial bar, hold 'b' to make it decrease.