Port away from HeaderFooterToolbar

When I created this component, I didn't know that the QQC2 `ToolBar`
component can do all the same things and even has built-in support for
being displayed as a header or a footer. So let's use that instead.
1 job for port-away-from-HeaderFooterToolbar in 19 seconds
latest
Status Job ID Name Coverage
  Build
passed #68473
reuse

00:00:19