Initialize crop aspect in GUI based on actual crop data.

This is a usability fix ensuring that the crop is not changed
because previous visited image had another aspect ratio.
Refine previous algorithm to find the aspect ration.

We now look for the closest known aspect ratio, if above a
certain epsilon we set to free aspect.
Add support for grain Lr import.
Add support for flip (orientation) Lr import.
Remove useless casting.
Refine previous algorithm to find the aspect ratio.
Merge branch 'po/lr-import'

* po/lr-import:
  Remove useless casting.
  Add support for flip (orientation) Lr import.
  Add support for grain Lr import.