Fix sort order when adding pictures

[clochix]

Mentioned in the forum: when the user drag and drop photos, they are added at the end of the album, but when he imported pictures from Files, it is added at the beginning. We should make this behavior more consistent.

[Thatoo]

We should be able to sort the picture in different ways (manualy, by date, by name...) after we import the pictures in the album!