Add "Original folder" to "Folders to search"

[Paruccone]

Feature Description
...
I'd like to be able to select an original folder containing all the files I want to be hashed and to search for their duplicates.

Use case scenario: I archive all of the videos I filmed on my NAS (original folder) and want to delete leftovers from other storages/folders without touching the archive.

Today it is possible to select a reference folder but this will only have an impact after analysis (will scan and hash all files of all folders to search). Selecting "Original Folder" would allow much faster results as it would only hash files in "Original Folder", scan and identify duplicates only within files in "Folders to search" that matched size and content (no need to scan/hash all the others).