feature: add option to also show other character set if different

[apttx]

searching something based on videos or subtitles can be hard if the source uses a different character set (f.e. traditional) than oneself (f.e. simplified).

• add a checkbox below the character set radio inputs that toggles a setting
  • storage key: settings/show_secondary_character_set_if_different (derive store & file names from this)
  • label: Also show traditional if different when simplified is selected as the primary set, otherwise Also show simplified if different