Allow histograms to be sampled or non-sampled

[ScottMansfield]

Histograms currently have a default of sampling at 25%, but some operations have much less volume than others and could be non-sampled. This would give the best fidelity possible for each situation. As well, if a histogram gets few enough observations we lose more accuracy by sampling than a histogram with many observations.

[ScottMansfield]

New thought: First pass would be to make the get histogram sampled and the rest not. Later on it could be valuable to have this configurable, but so far it doesn't seem like it.