title: Error Class 'kartik\widgets\SideNav' not found
body: <p>I have downloaded <code>yii2-widgets-master</code> and don't know where I should keep it.
  I am facing the error <code>Class kartik\widgets\SideNav</code> not found.</p>
  
  <p>My code is here</p>
  
  <pre><code>&lt;?php 
  use yii\helpers\Url;
  use kartik\widgets\SideNav;
  ?&gt;  
  &lt;div id = "links"&gt;
  &lt;div class="user-img"&gt;&lt;a href = "" class="user"&gt;&lt;i class="fa fa-user" aria- hidden="true"&gt;&lt;/i&gt;&lt;/a&gt;
  &lt;div class="text-center info"&gt;  &lt;p&gt;Wecare&lt;/p&gt;&lt;/div&gt;
  &lt;/div&gt;
  &lt;?php
  $menuItems[] =  ['label' =&gt; 'DFenX - Yii2 User - '. Yii::t('app','User Admin     Panel'),  'icon' =&gt; 'cog', 'url'=&gt;Url::to(['/user/admin/index'])];
  $menuItems[] =  ['label' =&gt; Yii::t('app','Authentication manager'),  'icon'    =&gt; 'th-list', 'items' =&gt;  [    
  ['label' =&gt; 'Settings', 'icon' =&gt; 'th-list', 'items' =&gt; [
  ['label' =&gt; '/user/settings',  'url'=&gt;Url::to(['/user/settings'])],
  ['label' =&gt; '/user/settings/profile',     'url'=&gt;Url::to(['/user/settings/profile'])],
  ['label' =&gt; '/user/settings/account',     'url'=&gt;Url::to(['user/settings/account'])],
  ['label' =&gt; '/user/settings/networks',   'url'=&gt;Url::to(['/user/settings/networks'])],
  ]],
  ['label' =&gt; 'Registration', 'icon' =&gt; 'th-list', 'items' =&gt; [                                
  ['label' =&gt; '/user/registration/register',     'url'=&gt;Url::to(['/user/registration/register'])],
  ['label' =&gt; '/user/registration/resend',    'url'=&gt;Url::to(['/user/registration/resend'])],
  ]],
  ['label' =&gt; 'Security', 'icon' =&gt; 'th-list', 'items' =&gt; [                                
  ['label' =&gt; '/user/security/login',   'url'=&gt;Url::to(['/user/security/login'])],
  ['label' =&gt; '/user/security/logout',    'url'=&gt;Url::to(['/user/security/logout'])],
  ]],
  ['label' =&gt; 'Recovery', 'icon' =&gt; 'th-list', 'items'  =&gt; [                               
  ['label' =&gt; '/user/recovery/request',    'url'=&gt;Url::to(['/user/recovery/request'])],
  ['label' =&gt; '/user/recovery/reset',   'url'=&gt;Url::to(['/user/recovery/reset'])],
  ]],
  ]];
  $type = SideNav::TYPE_PRIMARY;
  $heading = '&lt;i class="glyphicon glyphicon-user"&gt;&lt;/i&gt; ' . Yii::t('app','USER    Admin - UTILITIES');
  echo SideNav::widget([ 
  'type' =&gt; $type,
  'encodeLabels' =&gt; false,
  'heading' =&gt; $heading,
  'items' =&gt;$menuItems,
  ]);
  ?&gt;
  &lt;/div&gt;
  </code></pre>