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

spec/controllers/api/v1/accounts_controller_spec.rb

@@ -27,14 +27,11 @@ RSpec.describe Api::V1::AccountsController, type: :controller do
   describe 'PATCH #update_credentials' do
     describe 'with valid data' do
       before do
-        avatar = File.read(Rails.root.join('app', 'assets', 'images', 'logo.png'))
-        header = File.read(Rails.root.join('app', 'assets', 'images', 'mastodon-getting-started.png'))
-
         patch :update_credentials, params: {
           display_name: "Alice Isn't Dead",
           note: "Hi!\n\nToot toot!",
-          avatar: "data:image/png;base64,#{Base64.encode64(avatar)}",
-          header: "data:image/png;base64,#{Base64.encode64(header)}",
+          avatar: fixture_file_upload('files/avatar.gif', 'image/gif'),
+          header: fixture_file_upload('files/attachment.jpg', 'image/jpeg'),
         }
       end