mate-applets: update to 1.22.1

### mate-applets 1.22.1

  * update translations
  * Use g_list_free_full() convenience function
  * Fix use-after-free clang warning
  * help: update copyright
  * Help: Use XInclude instead of ENTITY for legal.xml
  * assignment discards 'const' qualifier from pointer target type
  * Make translatable documenters in about dialog
  * Make translatable copyright info in about dialog
  * Ensure proper translation of the about dialog title

(gutteridge)