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/features/compose/components/upload_button.js

@@ -0,0 +1,61 @@
+import React from 'react';
+import IconButton from '../../../components/icon_button';
+import PropTypes from 'prop-types';
+import { defineMessages, injectIntl } from 'react-intl';
+
+const messages = defineMessages({
+  upload: { id: 'upload_button.label', defaultMessage: 'Add media' }
+});
+
+
+const iconStyle = {
+  height: null,
+  lineHeight: '27px'
+}
+
+class UploadButton extends React.PureComponent {
+
+  constructor (props, context) {
+    super(props, context);
+    this.handleChange = this.handleChange.bind(this);
+    this.handleClick = this.handleClick.bind(this);
+    this.setRef = this.setRef.bind(this);
+  }
+
+  handleChange (e) {
+    if (e.target.files.length > 0) {
+      this.props.onSelectFile(e.target.files);
+    }
+  }
+
+  handleClick () {
+    this.fileElement.click();
+  }
+
+  setRef (c) {
+    this.fileElement = c;
+  }
+
+  render () {
+
+    const { intl, resetFileKey, disabled } = this.props;
+
+    return (
+      <div className='compose-form__upload-button'>
+        <IconButton icon='camera' title={intl.formatMessage(messages.upload)} disabled={disabled} onClick={this.handleClick} className='compose-form__upload-button-icon' size={18} inverted style={iconStyle}/>
+        <input key={resetFileKey} ref={this.setRef} type='file' multiple={false} onChange={this.handleChange} disabled={disabled} style={{ display: 'none' }} />
+      </div>
+    );
+  }
+
+}
+
+UploadButton.propTypes = {
+  disabled: PropTypes.bool,
+  onSelectFile: PropTypes.func.isRequired,
+  style: PropTypes.object,
+  resetFileKey: PropTypes.number,
+  intl: PropTypes.object.isRequired
+};
+
+export default injectIntl(UploadButton);