Blur effect on lower graphics settings

[jcfc]

We asked for this when blur was released but @zeuxcg said no

@zeuxcg

Blur with fewer samples is a bit faster but there’s some fixed cost you pay as well.
Pixelization could be faster depending on the approach.

But bottom line is - there is a cost and your players on really low-end hardware would appreciate your game more if it did not run at 20 FPS. And it may be impossible to get the blur to be performant enough - some cards are bad enough that they struggle to run a level with sky & baseplate & a few thousand parts at 30 FPS.