Covers non-document mode, tab icon, and adds a more
useable interface. Some parts are still missing, like
tab orientation and long tab titles.
Task-number: QTBUG-61092
Change-Id: Idbda84f513e3ff7f87fa04ae4476b11bd8bb6bf2
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>