[Qt, OSX] QProgressBar CPU-Issue workaround

fixes #5295
[Qt, OSX] move QProgressBarMac to guiutil.h
Merge pull request #5296

0ceab00 [Qt, OSX] move QProgressBarMac to guiutil.h (Jonas Schnelli)
6093aa1 [Qt, OSX] QProgressBar CPU-Issue workaround (Jonas Schnelli)