Make visutil_correctIvalsForDisplay obsolete

[BenjaminBlankertz]

As far as I remember, this function was introduced due to the following dilemma: On one hand time intervals, as returned by procutil_selectTimeIntervals, are use for feature extraction (e.g., proc_jumpingMeans), for indicating time intervals as labels (in plot_scalpEvolution?), and for shading intervals grid_markInterval (private function). There were probably conflicting requirements, which which unelegantly solved by introducing the aforementioned function.