[xy-chart] use babel instead of webpack to support deep imports

[williaster]

🏆 Enhancements

• This PR does a bit of refactoring in @data-ui/xy-chart so it's built with babel instead of webpack in order to support deep imports in addition to package-level imports.

  This should allow users to minimize bundle size by importing only the components they need instead of the entire package. Once webpack 4 comes out this will be moot, and we'll add the sideEffects flag to the package.json

// deep imports
import XYChart from '@data-ui/xy-chart/build/chart/XYChart';

// or, package-level
import { XYChart } from '@data-ui/xy-chart';

fixes #49
cc @lencioni

[coveralls]

Coverage remained the same at 84.457% when pulling 8114223 on chris--babelify-xy-chart into a2eae66 on master.

[coveralls]

Coverage decreased (-3.0%) to 81.481% when pulling 8114223 on chris--babelify-xy-chart into a2eae66 on master.

[lencioni]

If you don't have any side effects, I don't think there's any reason to wait adding that value to your package.json so it will be ready whenever people get on webpack 4.

Also, you probably should add an ESM build that avoids compiling your imports/exports into CommonJS, so tree-shaking can actually do its job (CommonJS deoptimizes tree-shaking, since tree-shaking is enabled by ES module semantics).

[williaster]

Abandoning this in favor of #111