This makes vertex paint match image painting more closely.
- Add falloff shape option sphere/circle
where sphere uses a 3D radius around the cursor and
circle uses a 2D radius (projected), like previous releases.
- Add normal angle option so you can control the falloff.
- Add Cull option, to paint onto faces pointing away.
Disabling normals, culling and using circle falloff
allows you to paint through the mesh.