- move more active properties into their collections:

  scene.active_keying_set --> scene.keying_sets.active
  ...same for active_uv_texture. active_vertex_color, active_keyconfig, 

- move mesh.add_uv_layer() and mesh.add_vertex_color() into their collections
  also have them return the newly created layer and dont set the layer active.

  uvtex = mesh.uv_layers.new(name)
  vcol = mesh.vertex_colors.new(name)