wallpapers/image: Refactor it and add autotests for the backend, all finders and models
More will come after this MR. No new feature is added.
Main changes:
- Split
BackgroundListModel
, now withImageListModel
andPackageListModel
(for KPackage wallpaper) - Move finders and models to its own folders
- Add autotests for all finders and models.
- Remove unused headers and functions
Edited by Fushan Wen