Add "robust" variance estimates

[multimeric]

Is your feature request related to a problem? Please describe.

Currently if you dataset contains outliers, it will skew the estimation of variance in the data, which makes the outliers in turn less obvious. If we provide the option to use a robust variance estimator (such as MinCovDet), we can avoid this issue.

Describe the solution you would like

I think on the trend plot we can simply add a checkbox that enables MCD variance.