Use upstream's Icon component

Rework the codebase to avoid unnecessary differences with upstream

app/javascript/flavours/glitch/components/icon.js

@@ -1,26 +1,21 @@
-//  Package imports.
-import classNames from 'classnames';
-import PropTypes from 'prop-types';
 import React from 'react';
+import PropTypes from 'prop-types';
+import classNames from 'classnames';
+
+export default class Icon extends React.PureComponent {
+
+  static propTypes = {
+    id: PropTypes.string.isRequired,
+    className: PropTypes.string,
+    fixedWidth: PropTypes.bool,
+  };
+
+  render () {
+    const { id, className, fixedWidth, ...other } = this.props;
+
+    return (
+      <i role='img' className={classNames('fa', `fa-${id}`, className, { 'fa-fw': fixedWidth })} {...other} />
+    );
+  }
 
-//  This just renders a FontAwesome icon.
-export default function Icon ({
-  className,
-  fullwidth,
-  icon,
-}) {
-  const computedClass = classNames('icon', 'fa', { 'fa-fw': fullwidth }, `fa-${icon}`, className);
-  return icon ? (
-    <span
-      aria-hidden='true'
-      className={computedClass}
-    />
-  ) : null;
 }
-
-//  Props.
-Icon.propTypes = {
-  className: PropTypes.string,
-  fullwidth: PropTypes.bool,
-  icon: PropTypes.string,
-};