Implement zooming for the compile output and app output panes.
Those windows can be zoomed by toolbar buttons or ctrl+mousewheel.
The zoom factor is synced between app output panes, but not between
compile and app output. The scroll wheel zoom can be disabled
in the settings.

While at it, fix that the AppOutputPane did not update its font
on changes to the fontsettings.

Task-number: QTCREATORBUG-12476
Change-Id: I8a1639ab3d39c24a5fc21ed82f558f3d10efc02d
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>