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

bin/yarn

@@ -0,0 +1,11 @@
+#!/usr/bin/env ruby
+VENDOR_PATH = File.expand_path('..', __dir__)
+Dir.chdir(VENDOR_PATH) do
+  begin
+    exec "yarnpkg #{ARGV.join(" ")}"
+  rescue Errno::ENOENT
+    $stderr.puts "Yarn executable was not detected in the system."
+    $stderr.puts "Download Yarn at https://yarnpkg.com/en/docs/install"
+    exit 1
+  end
+end