Update Global Theme and SDDM theme preview images for Milky Way

This is the new Plasma 5.21 wallpaper.

Update Global Theme and SDDM theme preview images for Milky Way
This is the new Plasma 5.21 wallpaper.
990048ed · Nate Graham · 34c1ac3f · 34c1ac3f · 990048ed · 34c1ac3f
Commit 990048ed authored Jan 05, 2021 by Nate Graham
--- a/lookandfeel/contents/previews/fullscreenpreview.jpg
+++ b/lookandfeel/contents/previews/fullscreenpreview.jpg
--- a/lookandfeel/contents/previews/lockscreen.png
+++ b/lookandfeel/contents/previews/lockscreen.png
--- a/lookandfeel/contents/previews/preview.png
+++ b/lookandfeel/contents/previews/preview.png
--- a/sddm-theme/preview.png
+++ b/sddm-theme/preview.png