Replace sprockets/browserify with Webpack (#2617)

* Replace browserify with webpack

* Add react-intl-translations-manager

* Do not minify in development, add offline-plugin for ServiceWorker background cache updates

* Adjust tests and dependencies

* Fix production deployments

* Fix tests

* More optimizations

* Improve travis cache for npm stuff

* Re-run travis

* Add back support for custom.scss as before

* Remove offline-plugin and babili

* Fix issue with Immutable.List().unshift(...values) not working as expected

* Make travis load schema instead of running all migrations in sequence

* Fix missing React import in WarningContainer. Optimize rendering performance by using ImmutablePureComponent instead of
React.PureComponent. ImmutablePureComponent uses Immutable.is() to compare props. Replace dynamic callback bindings in
<UI />

* Add react definitions to places that use JSX

* Add Procfile.dev for running rails, webpack and streaming API at the same time

config/webpack/configuration.js

@@ -0,0 +1,26 @@
+// Common configuration for webpacker loaded from config/webpack/paths.yml
+
+const { join, resolve } = require('path')
+const { env } = require('process')
+const { safeLoad } = require('js-yaml')
+const { readFileSync } = require('fs')
+
+const configPath = resolve('config', 'webpack')
+const loadersDir = join(__dirname, 'loaders')
+const paths = safeLoad(readFileSync(join(configPath, 'paths.yml'), 'utf8'))[env.NODE_ENV]
+const devServer = safeLoad(readFileSync(join(configPath, 'development.server.yml'), 'utf8'))[env.NODE_ENV]
+
+// Compute public path based on environment and CDN_HOST in production
+const ifHasCDN = env.CDN_HOST !== undefined && env.NODE_ENV === 'production'
+const devServerUrl = `http://${devServer.host}:${devServer.port}/${paths.entry}/`
+const publicUrl = ifHasCDN ? `${env.CDN_HOST}/${paths.entry}/` : `/${paths.entry}/`
+const publicPath = env.NODE_ENV !== 'production' ? devServerUrl : publicUrl
+
+module.exports = {
+  devServer,
+  env,
+  paths,
+  loadersDir,
+  publicUrl,
+  publicPath
+}