Attempt to support different collections of Unsplash
- I used Unsplash Source API (unlimited, public) instead of parsing HTML. It should be faster and more reliable. (Parsing HTML may break anytime they update their website...)
- Create UnsplashBaseProvider, which has collectionId in constructor. Extend it in children classes to support different collections. Now support all wallpaper collections.
Reviewers: Plasma, ngraham
Reviewed By: ngraham
Subscribers: ngraham, filipf, plasma-devel
Differential Revision: https://phabricator.kde.org/D22494