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_IMPORT_bmfile.py

@@ -8,7 +8,7 @@ class BBP_OT_import_bmfile(bpy.types.Operator, UTIL_file_browser.ImportBmxFile,
     bl_options = {'PRESET', 'UNDO'}
     
     @classmethod
-    def poll(self, context):
+    def poll(cls, context):
         return PROP_preferences.get_raw_preferences().has_valid_blc_tex_folder()
     
     def execute(self, context):