Mention completion for issue editor. (#3136)

* new issue mention

* Mention completion on new issue and view issue page.

* Code format.

* Require tribute in pull request page.

public/js/index.js

@@ -570,6 +570,7 @@ function initRepository() {
             if ($editContentZone.html().length == 0) {
                 $editContentZone.html($('#edit-content-form').html());
                 $textarea = $segment.find('textarea');
+                issuesTribute.attach($textarea.get());
 
                 // Give new write/preview data-tab name to distinguish from others
                 var $editContentForm = $editContentZone.find('.ui.comment.form');

public/vendor/plugins/tribute/tribute.css

@@ -0,0 +1,40 @@
+.tribute-container {
+  position: absolute;
+  top: 0;
+  left: 0;
+  height: auto;
+  max-height: 300px;
+  max-width: 500px;
+  overflow: auto;
+  display: block;
+  box-shadow: 0px 1px 3px 1px #c7c7c7;
+  z-index: 999999; }
+  .tribute-container ul {
+    margin: 0;
+    margin-top: 2px;
+    padding: 0;
+    list-style: none;
+    background: #ffffff; }
+  .tribute-container li {
+    padding: 8px 12px;
+    border-bottom: 1px solid #dcdcdc;
+    cursor: pointer; }
+    .tribute-container li.highlight, .tribute-container li:hover {
+      background: #2185D0;
+      color: #ffffff;}
+    .tribute-container li img {
+      display: inline-block;
+      vertical-align: middle;
+      width: 28px;
+      margin-right: 5px;
+    }
+    .tribute-container li span {
+      font-weight: bold; }
+    .tribute-container li span.fullname {
+      font-weight: normal;
+      font-size: 0.8rem;
+      margin-left: 3px;}
+    .tribute-container li.no-match {
+      cursor: default; }
+  .tribute-container .menu-highlighted {
+    font-weight: bold; }