Housekeeping Tasks

- [ ] Move "functional" operations from `geometry` to `geometry/functional`
- [ ] Move "functional" kernels (including ones for warping) from `geometry/kernel` to `geometry/functional/kernel`. This will include WarpUtilties.h, which may be used from within files in `geometry/kernel`.
- [ ] Move "functional" code and kernels from `rendering` to `rendering/functional`