Add suggest menu for user mentions in text editor

app/Formatter/UserMentionFormatter.php

@@ -0,0 +1,60 @@
+<?php
+
+namespace Kanboard\Formatter;
+
+/**
+ * Class UserMentionFormatter
+ *
+ * @package Kanboard\Formatter
+ * @author  Frederic Guillot
+ */
+class UserMentionFormatter extends BaseFormatter
+{
+    protected $users = array();
+
+    /**
+     * Set users
+     *
+     * @param array $users
+     * @return $this
+     */
+    public function withUsers(array $users) {
+        $this->users = $users;
+        return $this;
+    }
+
+    /**
+     * Apply formatter
+     *
+     * @access public
+     * @return array
+     */
+    public function format()
+    {
+        $result = array();
+
+        foreach ($this->users as $user) {
+            $html = $this->helper->avatar->small(
+                $user['id'],
+                $user['username'],
+                $user['name'],
+                $user['email'],
+                $user['avatar_path'],
+                'avatar-inline'
+            );
+
+            $html .= ' '.$this->helper->text->e($user['username']);
+
+            if (! empty($user['name'])) {
+                $html .= ' <small>'.$this->helper->text->e($user['name']).'</small>';
+            }
+
+            $result[] = array(
+                'value' => $user['username'],
+                'html' => $html,
+            );
+        }
+
+        return $result;
+    }
+}