paintopsettings refactoring

[LukasT.dev@gmail.com]

> It was mentioned on IRC that the measurement might be not accurate because
> it's done with a debug build.

No, the measurement is not done with debug build.
It is done with RelWithDebInfo build.

> I think the biggest performance improvement could be to optimize the case
> where the particles all have the same color.
> There you can write all particle shapes to a QPainterPath and pass that to
> fillPainterPath instead of doing one path per particle.
 
This case is not very common. You choose at least random opacity so that it 
looks cool. But I may give it a try.

I was interested more in the temporary paint devices. Any idea about that?