title: Django form with label directly in the Field, but disappear on typing
body: <p>I would like to achieve the same effect as google login page that the Label of the text field is shown in the field itself. When any characters is typed in the filed, the label automatically disappeared.</p>
  
  <p>I know how to achieve similar effect with html + java script, like:</p>
  
  <pre><code>&lt;input type="text" name="" id="" value="Email" class="gray"  onclick="if(this.value=='Email')
  {this.value='';this.className='black'}" onblur="if(this.value=='')    
  {this.value='Email';this.className='gray'}" /&gt;
  </code></pre>
  
  <p>But could django form does the same effect? I know I can specify <code>initial</code> in the CharField, but it won't disappear on typing.</p>
  
  <pre><code>forms.CharField(max_length=100, label=_("Email"), initial='xxx')
  </code></pre>