Refactor boolean expression
requested to merge 357-checkbox-show-trajectory-only-for-visible-people-working-incorrectly into master
The important change is from mControlWidget->isTrackShowOnlyVisibleChecked() to !mControlWidget->isTrackShowOnlyVisibleChecked() (Adding !)
But I refactored the boolean expression as a whole to be a bit more readable. (Other naming ideas for the variables are welcome though
Closes #357 (closed)