Darktable 4.6.0

What's new in this version:

- Editing history is now periodically auto-saved (every 10 seconds) while editing images in the darkroom view. The auto-save interval can be changed (via a preference) or auto-save can be disabled entirely (by setting the interval to 0).
- A new processing module rgb primaries has been added. This module can be used for delicate color corrections as well as creative color grading. It allows the red, green and blue primary colors to be moved around using "hue" and "purity" controls.
- The underlying pixel operation is essentially the same as channel mixing
- In addition, the sigmoid module now includes a new primaries section, which can be used to gracefully handle difficult lighting situations (e.g. LEDs) and tune the overall look of the image. Modifying these parameters can provide pleasing sunsets, improved skin tones etc. This feature can only be used with sigmoid's per-channel mode and is loosely based on ideas from Troy Sobotka's AgX and related work in the Blender community. The included "smooth" preset should provide a good starting point for further corrections using this feature.
- When working with the liquify and retouch modules, the full uncropped image is now always shown, with any crop indicated by displaying an overlaid rectangle. This allows for cropped-out parts of the image to be used without having to first disable the crop module and re-enable it when finished.
- When panning or zooming in the darkroom view, a low resolution placeholder used to be shown until the image was fully recalculated for the newly-visible region. Now, if any part of the previous view is still visible, that part will be immediately shown in high quality, with only the remainder of the image being temporarily shown in low quality until the pipe has finished.
- This has been achieved as part of a complete reworking of the darkroom image display, which has also removed some annoying jumps when replacing the low resolution placeholder with recalculated image data, or when switching between full and cropped view (when the crop, retouch or liquify modules are (un)focused).

Performance Improvements:
- OpenCL is now initialized in the background immediately after launching the darktable UI, with progress indicated by a series of toast messages. Previously, this was done before the main UI was launched, which could lead to significant delays (sometimes more than a minute) between the user opening darktable and anything appearing on-screen, making it appear as though darktable had failed to start. Note that processing will be slower (since darktable will only use the CPU) until OpenCL is fully initialized.
- An OpenCL code path has been implemented for lens correction using embedded correction metadata
- Image display speed in the map view has been increased by 25%
- Export speed has been improved for JPEG 2000 and B&W TIFF images
- The chromatic aberrations module is now approximagely 10% faster when run on the CPU