YACO (Yet Another CPU Overload)

[orenshatz]

When user is idle CPU usage should be as low as 4-8% (now that we instated the slice+render idle avoidance), but for some reason right now it's 15-25%. In other words, something's broken.

[orenshatz]

On Norbert's machine both the 4.1.2 release and the current master are 15% busy regardless of dataset and of whether segmentation is enabled. On my machine, without segmentation the j0126 itself is only ~7% as usual, but the corresponding 3D membrane boundary dataset is 25% for some reason. With segmentation even j0126 is 25% for me.