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/components/button.js

@@ -0,0 +1,50 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+
+class Button extends React.PureComponent {
+
+  constructor (props, context) {
+    super(props, context);
+    this.handleClick = this.handleClick.bind(this);
+  }
+
+  handleClick (e) {
+    if (!this.props.disabled) {
+      this.props.onClick();
+    }
+  }
+
+  render () {
+    const style = {
+      display: this.props.block ? 'block' : 'inline-block',
+      width: this.props.block ? '100%' : 'auto',
+      padding: `0 ${this.props.size / 2.25}px`,
+      height: `${this.props.size}px`,
+      lineHeight: `${this.props.size}px`
+    };
+
+    return (
+      <button className={`button ${this.props.secondary ? 'button-secondary' : ''}`} disabled={this.props.disabled} onClick={this.handleClick} style={{ ...style, ...this.props.style }}>
+        {this.props.text || this.props.children}
+      </button>
+    );
+  }
+
+}
+
+Button.propTypes = {
+  text: PropTypes.node,
+  onClick: PropTypes.func,
+  disabled: PropTypes.bool,
+  block: PropTypes.bool,
+  secondary: PropTypes.bool,
+  size: PropTypes.number,
+  style: PropTypes.object,
+  children: PropTypes.node
+};
+
+Button.defaultProps = {
+  size: 36
+};
+
+export default Button;