Document quartilemethod and "pre-computed" attributes for Box traces

[jdamiba]

a part of #2044

references work done in plotly/plotly.js#4432

• create example with q1/median/q3/lowerfence/upperfence/mean/sd/notchspan - https://codepen.io/etpinard/pen/gObgzdL?editors=1010

• create example with inclusive, exclusive, and linear quartile-computing algorithm - https://codepen.io/etpinard/pen/GRgrdyZ