Bundle Size Optimization Updates

[toddw]

1. Add support for webpack plugins. This allows us to use things like webpack's IgnorePlugin plugin and/or the ContextReplacementPlugin. (http://stackoverflow.com/questions/25384360/how-to-prevent-moment-js-from-loading-locales-with-webpack)
2. To better understand the bundle size, the webpack stats are now output to webpack-bundle-stats.json This file can be piped to webpack-bundle-size-analyzer like cat webpack-bundle-stats.json | webpack-bundle-size-analyzer for more detailed results.
3. Made react-router imports more specific as to not include parts of the library we are not using.

[christinebrass]

👍