All hail the new Background panel.
This is a minimal implementation. The idea is to build on top of it iteratively, since the designs themselves may change depending on how the interaction feels here.
This is how it looks right now:
- Switch to GListModel
- Make it use GtkFlowBox (requires 1)
- Draw the top bar/lock screen visuals on previews
- Button to add custom wallpapers
Fixes #515 (closed)