[Design spike] Namespacing config API

[jonvuri]

Spike on nesting / namespacing config parameters and breaking apart different config update methods to match.

Refer to comment #45 (comment), and some possible API examples from @biovisualize:

Config method for each sub-component

mapd3.Chart(container)
  .setBarChartConfig({...})
  .setAxesConfig({...})

Similar to event pattern:

chart1.getEvents()
  .onBrush("brushClear", callback)

Let the user compose the chart

const axis = mapd3.axis(container)
  .setConfig({})
  .onBrush(callback)
// ...
const chart = mapd3.composeChart(axis, bar, tooltip)

Simple, monolithic

mapd3.Chart(container)
  .setConfig({
    bar: {},
    axes: {}
  })