under windows on "create new", "further objects" you get the
native windows insert object dialog which has the "Display As Icon"
option, but on Linux etc (or using our own dialog) there isn't that
option

so add a "Display as icon" checkbox in our own dialog and generate
an icon through SvFileInformationManager::GetImage

Change-Id: I0a400189031900bd1e387465ec4ba57847cb5394