Minor code reorganisation.
Code refactoring to expose dt_ratings_apply_to_image.
Add support for importing rating from Lightroom XMP.
Add support for importing geo-tagging from Lightroom XMP.
Merge branch 'lightroom'

* lightroom:
  Add support for importing geo-tagging from Lightroom XMP.
  Add support for importing rating from Lightroom XMP.
  Code refactoring to expose dt_ratings_apply_to_image.
  Minor code reorganisation.