New GRASS vector editing in QGIS

Proof of concept of the new GRASS vector editing tools in QGIS:
- standard QGIS editing tools
- snapping to other layers
- undo and redo
- filled areas on background
- setting topological symbology in layer properties
- editing attributes using standard form
- symbology based on the edited attribute on background
- attributes form

A crowdfunding campaign to support implementation of these features will be launched in following weeks.