Apps: Round Corners, cleanups

Update a lot of app icons to use rounded corners (same as upstream).

Make a few adjustments for better sharpness, use updated gradients,
semi-transparent borders for better look in dark themes,
fit emblems inside squared icons better.

Add missing sizes where needed.

Fixed:
- `time-admin` - convert text to object, now renders better as PNG.
- Desktop Effects now uniform at all sizes, redid symlinks so they
  all point to `preferences-desktop-effects`.