feat: add light object support in importing virtools file.

- fix all `def poll(self)` to `def poll(cls)` to let it fit class method name convention.
- fix wrong progress counter when importing virtools file.
- add light support when importing virtools file.
- add corresponding conflict strategy and resolver for light.

bbp_ng/OP_UV_rail_uv.py

@@ -10,7 +10,7 @@ class BBP_OT_rail_uv(bpy.types.Operator):
     bl_options = {'UNDO'}
 
     @classmethod
-    def poll(self, context):
+    def poll(cls, context):
         return _check_rail_target()
 
     def invoke(self, context, event):