Plot recipes should accept `SamplingConstraint`s

[kahaaga]

Error bars are currently controlled by a two-element vector giving the quantiles to be plotted. We should keep this option, but the user should also be able to use the same syntax as when resampling (providing SamplingConstraints).

This is just a matter of implementing a few new recipes dispatching on SamplingConstraints instead of the vectors as they do now.