implement a box and whisker Shape

[davelandry]

Tasks include:

• [x] Whisker class
• [x] Box class
  • [x] config for the box itself
  • [x] config for the median
  • [x] uses Whisker class w/ pass-through config
  • [ ] draws outliers (data points that do not fit within the whisker extents)
  • [ ] supports changing orientation (ie. .orient("horizontal"))