Class-based system/import/index processor
Class-based system/import/html processor and delete not class-based
Some fixes to system/import/index processor
Fix issue #3975 and JSON-like import_element
Class-based system/import/html and index processor

* origin/pr/12135:
  Fix issue #3975 and JSON-like import_element
  Some fixes to system/import/index processor
  Class-based system/import/html processor and delete not class-based
  Class-based system/import/index processor