Port ShellBlurEffect and RedBorderEffect to paint nodes

Port the blur effect to the new ClutterEffect.paint_node() vfunc. Update the function names to match what they do, e.g. "apply_blur()" now creates the blur subtree and thus was appropriately renamed to "create_blur_nodes()".

There are 3 subtrees that can be generated by the blur effect:

1. Actor mode (full subtree; no cache)

      Root
       |
       |
    Layer (brightness)
       |
    Layer (horizontal blur)
       |
    Layer (vertical blur)
       |
    Layer (actor)
       |
    Transform (downscale)
       |
     Actor

2. Actor mode (partial subtree; cached contents)

      Root
       |
     Pipeline
  (final result)

3. Background mode

      Root
       |-----------------------
       |                       |
    Layer (brightness)        Actor
       |
    Layer (horizontal blur)
       |
    Layer (vertical blur)
       |
    Layer (background)
       |
      Blit

Depends on mutter!1340 (merged)