rename Design to Style in Web Wizard

Change-Id: I2b40f8a4d57199db80fc0defa35d71e81823295e
Reviewed-on: https://gerrit.libreoffice.org/11810
Reviewed-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>
Tested-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>