Manually specify order for samples in data/MC plot

[alexander-held]

Currently the sample order in the histogram stack follows from model.config.samples, with the first sample being the lowest in the stack. It would be useful to be able to customize this. Following the cabinetry config order would be an option, but only works if a config exists (not for standalone workspaces). Alternatively passing in a sorting function to be used with sorted(..., key=...) to the visualization could work.