ke_search 7.1.1

[TASK]    Refactor `getPiVars` to return by value and introduce `setPiVars`
[TASK]    Add nullability and default handling in `stripControlCharacters`. Thanks to r-herrmann. github.com/tpwd/ke_search/issues/323
[TASK]    Add strict typing and code cleanup in `FilterOptionHook`
[BUGFIX]  Skip PPT indexing when catppt is missing. Thanks to Christian Wolfram. github.com/tpwd/ke_search/pull/340
[BUGFIX]  Only create/update the filter option of the saved language when saving a localized system category. Thanks to Tobias Pinnekamp. github.com/tpwd/ke_search/issues/325