Improve emoji autocomplete dropdown

- Add a key to each list item so that Mithril's diffing algorithm is used correctly. This prevents the emoji images from remaining for half a second before they update to a new suggestion.
- Clean up styles. The `PostPreview` doesn't really belong here.

extensions/emoji/js/forum/dist/extension.js

@@ -202,19 +202,16 @@ System.register('flarum/emoji/addComposerAutocomplete', ['flarum/extend', 'flaru
               var imageName = (emojiMap[key].indexOf('-20e3') != -1 || emojiMap[key] == 'a9' || emojiMap[key] == 'ae' ? '00' : '') + emojiMap[key];
               return m(
                 'button',
-                { className: 'PostPreview',
+                {
+                  key: key,
                   onclick: function () {
                     return applySuggestion(code);
                   },
                   onmouseenter: function () {
                     dropdown.setIndex($(this).parent().index());
                   } },
-                m(
-                  'span',
-                  { className: 'PostPreview-content' },
-                  m('img', { alt: code, 'class': 'emoji', draggable: 'false', src: '//cdn.jsdelivr.net/emojione/assets/png/' + imageName + '.png' }),
-                  key
-                )
+                m('img', { alt: code, 'class': 'emoji', draggable: 'false', src: '//cdn.jsdelivr.net/emojione/assets/png/' + imageName + '.png' }),
+                key
               );
             };
 
@@ -340,7 +337,7 @@ System.register('flarum/emoji/components/AutocompleteDropdown', ['flarum/Compone
               this.props.items.map(function (item) {
                 return m(
                   'li',
-                  null,
+                  { key: item.attrs.key },
                   item
                 );
               })

extensions/emoji/js/forum/src/addComposerAutocomplete.js

@@ -68,15 +68,14 @@ export default function addComposerAutocomplete() {
             const code = ':' + key + ':';
             const imageName = (emojiMap[key].indexOf('-20e3') != -1 || emojiMap[key] == 'a9' || emojiMap[key] == 'ae' ? '00' : '') + emojiMap[key];
             return (
-              <button className={'PostPreview'}
+              <button
+                key={key}
                 onclick={() => applySuggestion(code)}
                 onmouseenter={function() {
                   dropdown.setIndex($(this).parent().index());
                 }}>
-                <span className="PostPreview-content">
-                  <img alt={code} class="emoji" draggable="false" src={'//cdn.jsdelivr.net/emojione/assets/png/' + imageName + '.png'}></img>
+                  <img alt={code} class="emoji" draggable="false" src={'//cdn.jsdelivr.net/emojione/assets/png/' + imageName + '.png'}/>
                   {key}
-                </span>
               </button>
             );
           };
@@ -88,7 +87,7 @@ export default function addComposerAutocomplete() {
             const fuzzyRegexp = function(str) {
               const reEscape = new RegExp('\\(([' + ('+.*?[]{}()^$|\\'.replace(/(.)/g, '\\$1')) + '])\\)', 'g');
               return new RegExp('(.*)' + (str.toLowerCase().replace(/(.)/g, '($1)(.*?)')).replace(reEscape, '(\\$1)') + '$', 'i');
-            }
+            };
 
             const regTyped = fuzzyRegexp(typed);
             for (var i=0, maxSuggestions = 7; i < emojiKeys.length && maxSuggestions > 0; i++) {
@@ -102,7 +101,7 @@ export default function addComposerAutocomplete() {
               return a.length - b.length
             });
 
-            for(let key of similarEmoji) {
+            for (let key of similarEmoji) {
               suggestions.push(makeSuggestion(key));
             }
 

extensions/emoji/js/forum/src/components/AutocompleteDropdown.js

@@ -10,7 +10,7 @@ export default class AutocompleteDropdown extends Component {
   view() {
     return (
       <ul className="Dropdown-menu EmojiDropdown">
-        {this.props.items.map(item => <li>{item}</li>)}
+        {this.props.items.map(item => <li key={item.attrs.key}>{item}</li>)}
       </ul>
     );
   }

extensions/emoji/less/forum/extension.less

@@ -11,28 +11,18 @@ img.emoji {
   position: absolute;
   margin: 5px 0 !important;
 
-  > li > a {
-    white-space: normal;
-    border-bottom: 0;
-  }
-
-  > li > a:hover {
-    background: none;
-  }
-
-  .PostPreview {
+  > li > button {
     color: @text-color;
     font-weight: bold;
+    padding-top: 6px;
+    padding-bottom: 6px;
+    padding-left: 45px;
 
     .emoji {
-      margin-right: 5px;
+      float: left;
+      margin-left: -30px;
     }
   }
-  .PostPreview-content {
-    overflow: hidden;
-    line-height: 1.7em;
-    display: block;
-  }
 }
 
 .ComposerBody-emojiWrapper {