add findExtremes
add findExtremes

- a Axes.expend clone that does not append things to ax._min/ax._max,
  but instead returns two arrays, a min array and max array
  of potential data extremes

etpinard/plotly.js,etpinard/plotly.js,aburato/plotly.js,asolagmbh/plotly.js,plotly/plotly.js,etpinard/plotly.js,plotly/plotly.js,plotly/plotly.js,asolagmbh/plotly.js,asolagmbh/plotly.js,plotly/plotly.js,aburato/plotly.js