Startcenter: Refresh RecentDocsView when select 'Clear list' menu option

Change-Id: I9cbe647563699b9b610661003084d2cd16093f9a
(cherry picked from commit d930cefbe65d8b7f21100fcbf2ddcd977dd15cb1)
Reviewed-on: https://gerrit.libreoffice.org/7304
Reviewed-by: Jan Holesovsky <kendy@collabora.com>
Tested-by: Jan Holesovsky <kendy@collabora.com>