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

app/views/layouts/embedded.html.haml

@@ -3,6 +3,6 @@
   %head
     %meta{:charset => 'utf-8'}/
     = stylesheet_link_tag 'application', media: 'all'
-    = javascript_include_tag 'application_public', integrity: true, crossorigin: 'anonymous'
+    = javascript_pack_tag 'public', integrity: true, crossorigin: 'anonymous'
   %body.embed
     = yield