Mipmap cache: prepare for border cropping for (downsampled) floating point buffers [X-Trans]

FIXME: do actually flip filter acc. to rawprepare iop crop x,y
rawprepare: border cropping for floating point buffers
rawprepare: set IOP_TAG_DISTORT, implement distort_(,back}transform
Deflicker (histogram of: source raw data): fix (crop)
Lens IOP: get_autoscale(): fix (crop)
Focus detection: fix
x,y are taken from pre-cropped thumbnail, so we need to "uncrop" them because dt_dev_distort_transform_plus will crop them back

FIXME: verify this!
dt_imageio_open_rawspeed(): break everything! Stop scaling (B/W).
rawprepare: scaling for raw mosaic buffers
rawprepare: scaling for floating point buffers
Deflicker (histogram of: source raw data): fix (no scaling)
Disable "Create HDR": FIXME: this function needs adapting (cropping + scaling (B/W))
iop_dependencies.py: add rawprepare
Run iop_dependencies.py after merge!
rawprepare: prepare for using blackLevelSeparate
rawprepare: raw mosaic: sepBlack
Rawprepare IOP: GUI

FIXME: add GUI for cropping params.
[FIXME] rawprepare: scaling for raw mosaic buffers [SSE]
rawprepare: scaling for floating point buffers buffers [SSE]
Rawprepare iop: implement OpenCL kernel (1f)!
Rawprepare iop: implement OpenCL kernel (4f)!