Fixed color palette for row/column annotation

[rdewijn]

Colors for annotation bars are now random

[plinders]

We found an issue that sometimes the number of colors in the color palette is less than the number of levels in the column/row annotation. This means that the same color is used for multiple levels. This happens randomly, can it be added that it selects a number of unique colors depending on the number of levels in the factor?

[rdewijn]

@fnaji : I think we should implement a fixed colour palette for row and col annotation.

Note that the number useful colours in a categorical palette is limited (8-12) , so with a large number of levels in the annotation use of same colour for multiple levels (@plinders ) cannot be prevented.