Invert y axis

[john-guerra]

For visualizing rankings, we want to be able to invert the y axis

[john-guerra]

This could be done using the yScale attribute, but then we should avoid overriding the domain and range when a yScale is provided. e.g.

TimeSearcher(data, {
  x: (d) => d[xVar],
  y: (d) => d.value,
  id: (d) => d.schoolcode,
  yScale: () => d3.scaleLinear().domain([100, 0])
})

[ivelascog]

implemented in #32