Feature/colorpicker

Example:

![zehge5de3cnhhrqw4okruws2mfjbfhtcysac8idol0e](https://f.cloud.github.com/assets/117409/2028396/c722024c-88cd-11e3-9e79-d75e3da7d332.png)

Usage:
```php
$builder->add('yourColorPickerField', 'color')
```