fdo#80538 Show an infobar when document is in read-only mode

and remove the Edit icon from the toolbar

Change-Id: I27d9506bd0fb76b3f1ad056a9866f7744674a3e2
Reviewed-on: https://gerrit.libreoffice.org/11182
Reviewed-by: Bosdonnat Cedric <cedric.bosdonnat@free.fr>
Tested-by: Bosdonnat Cedric <cedric.bosdonnat@free.fr>