Add centering at median for the EnsembleSummary

[jlperla]

The following code seems to work,, though I would want to make sure you like the naming and approach before adding tests/etc.

import DiffEqBase: EnsembleSummary
function DiffEqBase.EnsembleSummary(sim::DiffEqBase.AbstractEnsembleSolution{T,N},
                         t=sim[1].t;quantiles=[0.05,0.95], centermedian = false) where {T,N}
  if typeof(sim[1]) <: DiffEqBase.DESolution
    m,v = timeseries_point_meanvar(sim,t)
    med = timeseries_point_median(sim,t)
    qlow = timeseries_point_quantile(sim,quantiles[1],t)
    qhigh = timeseries_point_quantile(sim,quantiles[2],t)
  else
    m,v = timeseries_steps_meanvar(sim)
    med = timeseries_steps_median(sim)
    qlow = timeseries_steps_quantile(sim,quantiles[1])
    qhigh = timeseries_steps_quantile(sim,quantiles[2])
  end

  trajectories = length(sim)
  DiffEqBase.EnsembleSummary{T,N,typeof(t),typeof(m),typeof(v),typeof(qlow),typeof(qhigh)}(t,centermedian ? med : m,v,qlow,qhigh,trajectories,sim.elapsedTime,sim.converged)
end

As another interfacepoint, the quantiles argument takes in an array, but only works ones of length two. Perhaps it should be a tuple to avoid giving the impression that you can pass in more than 2.

[ChrisRackauckas]

Yeah, that seems like an agreeable change.