Show histograms of selected quantitative sample metadata fields as an alternative to the "sample presence information" table

The current sample presence info tables are great for summarizing categorical metadata, but they don't scale well to quantitative fields (e.g. pH). It would be really cool if we could add an option to show a histogram for the selected tip / internal node that, for each sample containing the node or its descendants, shows the distribution of values for a selected sample metadata field.

I think getting an early version of this up using [Vega-Lite](https://vega.github.io/vega-lite/examples/histogram.html) wouldn't be too bad.

Start by locating the existing sample presence information tables and reviewing the linked Vega-Lite histogram example. Define how a selected tip or internal node and quantitative sample metadata field feed the histogram, then verify that an option displays the value distribution for samples containing that node or its descendants.

Written by the indexing model from the issue text.