- Use new splash by Tyson Tan (optimized with `oxipng`).
- Refactor splash screen to use a PNG embedded as QRC.
- Include only a high res splash (960 px tall) and scale it when needed.
- Change splash image to be shown at 480 px tall in the splash and
  320 px tall in the about dialog (high-DPI scaled logical px).
- Render Krita logo with version branding and the "KRITA" text using
  QSvgWidget instead of having them inside the image.
- Dummy out the holidays splash for now.