Features/uat 154 absolute heatmap color mapping

All three heatmaps analyses have been made consistent in the way they map values to colors in the heatmap plot. The input argument color.range.clamps defines which values correspond to the extreme colors (bright green and red) of the color range. By default these are set to [-2.5, 2.5], but when color.range.clamps is set to NULL, the color range will be from the overall minimum and maximum values of the data to be plotted.