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/development.js

@@ -0,0 +1,16 @@
+// Note: You must restart bin/webpack-dev-server for changes to take effect
+
+const merge = require('webpack-merge')
+const sharedConfig = require('./shared.js')
+
+module.exports = merge(sharedConfig, {
+  devtool: 'sourcemap',
+
+  stats: {
+    errorDetails: true
+  },
+
+  output: {
+    pathinfo: true
+  }
+})