WallpaperPicker: bring back cm wallpapers

Change-Id: I41878885c6a88a2acaba26c1fba101b02940a360
Signed-off-by: Joey Rizzoli <joey@lineageos.it>
(cherry picked from commit d1bc43f5)

Fix bad wallpaper preview image format

* The image extension was .jpg but the image was actually png
  Convert it to jpg like all other wallpapers

Change-Id: I86a8dd6c254184a2b9069f7af693a4b3c0c08285

Change-Id: I41878885c6a88a2acaba26c1fba101b02940a360