Output a DNG file with the same layout as the inputs.
Several fixes to support more cameras.

- Keep the original black and white levels in the output file. Some raw developers make assumptions
  about them instead of reading them from the DNG tags.
- Add the MaskedAreas or BlackLevels tags so that black levels are correctly calculated.
- Avoid the ColorMatrix1 tag if it has not a correct value, even if that breaks the DNG standard.
- Generate automatic white balance coefficients when they are not provided.
- Fix repainting affected area after undo/redo, by rotating it first to its correct position.
- For now, do not save the frame to the output DNG until RawTherapee's issue 2413 is fixed.
Update README, add features for v0.4.4