Refactor the resource histogram and the resource utilization views

[arcady-zherdev]

1. Need to make a new base class on the Scheduler level that would allow to display histograms for an arbitrary store records
2. The class should support grid Group and TreeGroup features and provide API to aggregate rows data and display histogram for group level records
3. ResourceHistogram class should be changed to subclass that new base class and use its grouping API to display histograms for group levels (for Group and TreeGroup features).
4. ResourceUtilization class should be also changed to support the new grouping API and thus support Group and TreeGroup features.