auto scale histogram interval

[nreese]

Add an option to enable histogram interval auto scaling.

Static histogram intervals do not provide the flexibility required to explore data as filters are applied to the histogram field. Instead of seeing more details, visualizations are left with only one or a small number of buckets. It would be useful if the interval would automatically scale to provide a useful number of buckets (50ish) as the range imposed by a filter restricts the values of the histogram field.

[Bargs]

It was pointed out to me that this is actually a dupe of another older ticket: #3757