Add a lightable/darkroom mode to Lr import.

Typically tags are imported in lightable when importing a file or folder
and development processes when entering the first time an image.
Get image width/height from Lr xmp.

This is better as we do not need to have the dev->image_storage fully
intialized. We can then use the import routine sooner in the process.
Do not try to free a null pointer.
Add auto mode in lightroom.

This mode is used when auto-importing tags in lightable or develop
processes in darkroom.
If no dt sidecar found, check for lr one.

At this stage we only import the tags.
Import lr develop process the first time we visit an image.
Revert "Add Lr cairo button for the import from Lr support."

This reverts commit 01861d50b9561f8a980247efcc8b0969c7fa3e5c.
Remove Lr button from darkroom.
Check that the XMP has really been produced by Lightroom.
Better handling of translation for plural form.
Load lr develop only when loading the image.

Do not load the develop process when loading preview for example.

to be squashed: 5e52ce6
                Import lr develop process the first time we visit an image.
Handles all the orientations as defined in the tiff:Orientation node.

Previously only the landscape orientations were taken into account.