Closes #152

Tasks

• Implement material.color_mode for mesh, meshslice, line, and point.
  • Options are 'uniform', 'vertex', 'face', 'vertex_map' and 'face_map'.
  • With 'vertex' and 'face, the geometry.colors` are used.
  • With 'vertex_mapandface_map, the geometry.texcoordsare used, and then looked up intomaterial.map`.
  • Also has 'auto' which means use 'uniform' unless the material has a .map, in which case use vertex_map.
• Meshslice now supports all color modes (previously only uniform color).
• Lines now also support face colors, which means the line-pieces can be individually colored.
• The material.vertex_colors flag raises a deprecationwarning for now.
• The mesh material.face_colors (added in Quad drawing in Mesh Shader, when the input index has shape(nx4) #529) is simply removed.
• Fixed that the anti-aliased fragments were previously dropped because of an incorrect render_mask.
  • This makes the points look slightly larger (i.e. they were a bit too small earlier).

Notes on aa

• The mesh shader does not use aa, so a mesh with an opaque color is fully opaque.
• Same for mesh slice at the moment.
• Lines uses aa, so they always have transparent fragments.
• Same for points. However, the render_mask was previously set to ignore the transparent fragments, which can be considered a bug.
• Text also uses aa.