Add octave_link uiputfile implementation * libgui/src/dialog.cc, libgui/src/dialog.h (FileDialog::FileDialog): Change bool multiselect to QString multimode, add mode option of 'create' and set options accordingly. (QUIWidgetCreator::signal_filedialog): Change bool multiselect to QString multimode. (QUIWidgetCreator::create_filedialog): Change bool multiselect to QString multimode. * libgui/src/main-window.cc, libgui/src/main-window.h (main_window::connect_uiwidget_links): update bool multiselect to QString multimode. (main_window::handle_create_filedialog): update bool multiselect to QString multimode. * libgui/src/octave-qt-link.h (octave_qt_link::do_file_dialog): update bool multiselect to std::string multimode. * libinterp/interpfcn/octave-link.h (octave_link::do_file_dialog): update bool multiselect to std::string multimode. (octave_link::file_dialog): update bool multiselect to std::string multimode. * scripts/plot/uiputfile.m (uiputfile): update to call __octave_link_file_dialog__ if octave_link is present.