in plotHeatmap need to give default colors to all factor entries of sampleData

[epurdom]

Currently, we only assign default colors if is.null(colorLegend) in the matrix version of plotHeatmap. If colorLegend is given, but doesn't give colors to all factors, then it is ignored and passed through to aheatmap. However, aheatmap doesn't recycle colors and can run out of colors! Which will mean that the levels will be white (in addition to aheatmap not having great colors). So need a default assignment to all factors to be added.

[epurdom]

Currently added this information to documentation of plotHeatmap telling user to define colors with clusterLegend if there are many factors/levels. If fix this problem, should remove this warning.