Add parallel projection camera setting.
Quick trace now shows parallel projection.

- Full trace now uses Camera#calcViewRay to initialize rays.
- Scene#quickTrace and pathTrace now interpret rays the same way.
- Field of view is only clamped when used to calculate non-parallel rays,
  rather than by the UI.
- Related comment updates and related refactoring.
Update parallel projection checkbox on scene load.
Remove extraneous whitespace and comment.
Add command-line help text and -scene-dir parameter.
Merged TOGoS parallel projection