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/javascript/mastodon/api.js

@@ -0,0 +1,26 @@
+import axios from 'axios';
+import LinkHeader from './link_header';
+
+export const getLinks = response => {
+  const value = response.headers.link;
+
+  if (!value) {
+    return { refs: [] };
+  }
+
+  return LinkHeader.parse(value);
+};
+
+export default getState => axios.create({
+  headers: {
+    'Authorization': `Bearer ${getState().getIn(['meta', 'access_token'], '')}`
+  },
+
+  transformResponse: [function (data) {
+    try {
+      return JSON.parse(data);
+    } catch(Exception) {
+      return data;
+    }
+  }]
+});