I've added a parallel projection setting.

I've added a 'Parallel Projection' checkbox on the Camera tab which, when checked, causes the Camera to interpret the field of view as meters offset (if fov = 64, it'll start rays 32 meters from the origin in the Y-plane, and aspect ratio * 32 in the X) rather than degrees.  I also changed the place at which the ray is munged so that it is more consistently munged by quickTrace and pathTrace, changed RenderWorker#work to use Camera#calcViewRay to initialize rays for both the quick and full render, and modified some comments.

I am not sure if I am setting up the controls in buildCameraPane under setHorizontalGroup correctly, or how that actually gets used.

The commits relating to parallel projection are up to 2e871ee.  After that are some changes I'm working on for better command-line support.