render: bloom using multiple smaller size buffers

[kikonen]

Change bloom to use same logic as blur for emission.

Perhaps should consider if there is need to have them separately at all.

Reason for being separate passes is that they do a bit differerent thing. I.e. emission doesn't mean "over burning" image, but just glow emission, which does not imply overly bright color. While bloom is only for overly bright colors.

i.e. emission could end up bloomed, if some "emission strenght" multiplier is used for it.