Improve blur behaviour and make navigation bar transparent

1. Use cached blur wallpaper instead of live blurring for smooth visual effects.
2. Make Navigation Bar transaprent to match with bottom dock.
3. Use transparent grey color as background for folder icons.
4. Use placeholder in case wallpaper is not available.
3 jobs for blur-background in 7 minutes (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #80276
build

00:07:00

failed #58180
build

00:05:44

failed #58185
build

00:04:32