Duplicates Reference Image selection

Problem description

In version below 8.0.0-beta1 when searching for duplicates it is not possible to choose, which image is the reference image (TODO: find out how it will be determined)

In the current time the photos are stored on multiple storages phone sd card, internal memory but might be also synched into the cloud. A second point is backuping all photos but keeping them on the phone. In this scenario at the next backup all photos have to be checked if they aren't yet in the collection or not. This is illustrated in the following image. The folder "potentialDuplicates" indicates a folder with all imported photos and the "collection" folder and the folders below contain the sorted photos. After all duplicates are found with the "Remove Duplicates" Button the duplicates can be removed. But in this case image-1.jpg, image-2.jpg are kept and in the sorted collection the photo will be deleted which is not desired, because then the photo has to be sorted in again.

The idea of this merge request is to give the user an option to choose which method should be used to determine the reference image. Potential methods:

• the user selects a folder with unsorted photos which shall not be used as references
• the user selects a folder with should be preferred as reference
• ...

Problems:

• If the selected method is "prefer Folder" and the selected folder has subfolders, only the images in the main folder are used, but not from the ones below Handling in !209 (merged)

• The reference image selection method in the combobox will not be stored/restored yet

• If a folder is selected, the subfolders are not selected. if "whole collection" is selected, also the subfolders are selected Handling in !209 (merged)

• Testing what happens if for both "whole collection" is selected. Only one of the duplicates shall be the reference!