Blurb:: type of statistical metric roll-up for multifidelity UQ methods

Description:: When performing adaptive refinement in multifidelity UQ
methods, one can adapt the expansion for a model level/fidelity based
on its local statistics (\c active) or based on the statistics for the
aggregate expansion (\c combined).  The latter case may incur
additional computational overhead, but ensures that the refinement
occurs in the aggregate multifidelity context.

<b> Default Behavior </b>

Default for multifidelity methods is \c combined statistics.

<b> Expected Output </b>

<b> Usage Tips </b>

<b> Additional Discussion </b>

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