* Redesigned alpha blending and paint drying algorithms. Now it gives much better results when using low brush alpha or when surface has initial color set.
* Fix: "Slow" dissolve/dry was scaled incorrect when using substeps. Also adjusted time to better match non-"slow" setting.
* Fixed possible issues when using image textured brush.
* Fix: particle brush panel was no longer visible since last commit.
* Adjusted default surface values.
* Some more code cleanup.
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