Calculate heatmap values per group

[BasLee]

Fix the percentage and color intensity of heatmap cells in the group comparision clinical attributes heatmap.

Groups most often do not have the same number of samples. In the old heatmap the value of the buckets or cells where calculated as fraction = samples in bucket / max number of samples in all groups. This should be: fraction = samples in bucket / max number of samples in current group. Now we can compare the fraction (displayed as percentage) across groups.

In addition the color intensity is now scaled to the highest fraction across the groups in order to use the full color spectrum available.