Webpack3 build and local dev server

[zmaybury]

Upgrade WeaveApp to use Webpack3 for transforming, bundling, and packaging WeaveApp and required dependencies.

Webpack3 will do everything the current build process does, but will also allow for more flexibility in the code. For example, css, images, and other files can now be imported using ES6, and will be bundled directly with the code. Additionally, production plugins can be included to drastically reduce asset size, automatically uglify and minify the JS while maintaining source maps, and can provide visualizations about the structure of the application.

Additionally, Webpack3 enables the use of a local development server, which can build the application and serve it on your local machine, as well as incrementally build and hot reload the application when changes are made. This should greatly ease/speed local development, as no tomcat server will be required for local dev, and hot reloading will not require a full rebuild of the application to see changes.