title: Custom form field type in Symfony
body: <p>I have an entity with an array field data (doctrine array). I want to create a symfony form for this entity and i would like include this field in it. </p>
  
  <p>So, the question is:
  Is there any way to use custom type as form field in Symfony?</p>
  
  <p>This is form field:</p>
  
  <pre><code>/**
   * @var array
   *
   * @ORM\Column(name="dates", type="array")
   */
  private $dates;
  </code></pre>
  
  <p>This is formType:</p>
  
  <pre><code> public function buildForm(FormBuilderInterface $builder, array $options)
      {
          $builder
              -&gt;add('dates') // i want to use -&gt;add('dates','array') but type 'array' is not allowed
          ;
      }
  </code></pre>
  
  <p>This is data i want to save:</p>
  
  <pre><code>$dates = array(
          'birthday' =&gt; \DateTime('1995'),
          'wedding' =&gt; \DateTime('2001'),
          // and so on
      )
  </code></pre>