Flag newly rotated images to be scanned for faces

Just a small improvement: This merge request flags images that have been rotated by the user so that they can be scanned for faces again in the future.

Use case: A user adds images to Digikam and scans the images for faces using the Face Recognition feature. Afterwards, the user realises that some images need to be rotated correctly (there could be several reasons why the original images are not rotated correctly). Since the images were scanned for faces with the wrong orientation, it is very likely that faces were not correctly detected. Therefore, this merge request implements, that images are flagged to be scanned for faces in future face-detection tasks whenever the user rotates them.