registration.qtildematrices: operate on transforms

Instead of taking subband tuples directly, refactor qtildematrices to
take transforms and warp them via an warptransform function. This is an
effort to tidy up the public API to make it easier to fit OpenCL in
later. Make warphighpass internal-only.
remote image-registration-1.py example

The code in image-registration-1.py was no longer exemplary of
best-practice. Remove it rather than letting it bit rot.
examples/image-registration: save figures and include in docs
registration: remove older affine... functions

Nothing uses these functions any more so don't let them bitrot
registration: limit public API

Remove a lot of the internal functions from the public API. We can
always add them later if people want them and they can still be
import-ed.
registration: fix default method for warp
split registration into explicit numpy backend