ModelSelection to support multiple estimators and multiple datasets

[elphick]

Presently ModelSelection can support only multiple (e) estimators, OR multiple (d) datasets.
These are presented as boxplots.
If e x d is provided, we would like a heatmap of the mean/median results.
Solutions for a visual indicator of variance/range in the heatmap would be ideal.

[elphick]

The processing of cases now supports the multiple (d x e) situation. Now need:

1. Some error handling on existing plots for (1 x e) and (1 x d) case (boxplot).
2. A heatmap plot for the (d x e) case.