RFE: Port the Chimera lighting GUI

[Zach Pearson]

We're closer than ever to releasing our new raycasting rendering mode. We started this project with better lighting in mind, so I expect that users will want to change the lighting often depending on the model they're looking at. The lighting command is not too intuitive to use; without the center of rotation model up it's hard to know your orientation in the world, then even after you get your bearings you as the user have to know how to angle the light vector relative to your model with the command 'lighting direction x,y,z'. The lighting GUI from Chimera was really intuitive, and I think users will have a better experience using it than the command.

[Zach Pearson]

There's a pretty good prototype in the existing (but not installed by default) lighting_gui bundle