• Implement algorithms for the marker brush
• Connected marker brush algorithm to the brush itself
• Implement a GUI for the round brush configuration
• Limit the brush size of the roundmarker
• Fix HUD properties for Roundmarker brush

Merge remote-tracking branch 'origin/master' into kazakov/round-marker
Ref T3492

Just try to paint with the new branch and tell what you think about it!

1. It cannot vary its opacity during the stroke
2. It has no fading (like usual marker)
3. Brush dialog is limited, that is expected. The only features that can be implemented are: scatter and texturing.

You can also use a git branch: kazakov/round-marker