Add emoji autosuggest (#5053)

* Add emoji autosuggest

Some credit goes to glitch-soc/mastodon#149

* Remove server-side shortcode->unicode conversion

* Insert shortcode when suggestion is custom emoji

* Remove remnant of server-side emojis

* Update style of autosuggestions

* Fix wrong emoji filenames generated in autosuggest item

* Do not lazy load emoji picker, as that no longer works

* Fix custom emoji autosuggest

* Fix multiple "Custom" categories getting added to emoji index, only add once

app/javascript/mastodon/components/autosuggest_emoji.js

@@ -0,0 +1,37 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+import { unicodeMapping } from '../emojione_light';
+
+const assetHost = process.env.CDN_HOST || '';
+
+export default class AutosuggestEmoji extends React.PureComponent {
+
+  static propTypes = {
+    emoji: PropTypes.object.isRequired,
+  };
+
+  render () {
+    const { emoji } = this.props;
+    let url;
+
+    if (emoji.custom) {
+      url = emoji.imageUrl;
+    } else {
+      const [ filename ] = unicodeMapping[emoji.native];
+      url = `${assetHost}/emoji/${filename}.svg`;
+    }
+
+    return (
+      <div className='autosuggest-emoji'>
+        <img
+          className='emojione'
+          src={url}
+          alt={emoji.native || emoji.colons}
+        />
+
+        {emoji.colons}
+      </div>
+    );
+  }
+
+}