Trace data is saved in the background, progress is emitted, and
the save operation can be canceled. While data is being saved
the views are disabled and a semitransparent layer is put on top
of the trace view.

Task-number: QTCREATORBUG-11822
Change-Id: I94ec93147fb1788fc85939ddc591961d058050b5
Reviewed-by: Ulf Hermann <ulf.hermann@theqtcompany.com>