Magento – Custom Field Value not saving on sales_flat_quote & sales_flat_order

I have created a custom field from sales_flat_quote & sales_flat_order tables and in checkout page have field called delivery_date. When an order is being placed, it's not saving my custom field value.

My code is:

etc/modules/Easylife_Ats.xml

<?xml version="1.0"?>
<config>
    <modules>
        <Easylife_Ats>
            <active>true</active>
            <codePool>local</codePool>
        </Easylife_Ats>
    </modules>
</config>

Ats/etc/config.xml

<?xml version="1.0"?>
<config>
    <modules>
        <Easylife_Ats>
            <version>0.1.0</version>
        </Easylife_Ats>
    </modules>
    <global>
        <models>
            <ats>
                <class>Easylife_Ats_Model</class>
                <resourceModel>ats_resource</resourceModel>
            </ats>
            <ats_resource>
                <class>Easylife_Ats_Model_Resource</class>
            </ats_resource>
        </models>
        <blocks>
            <ats>
                <class>Easylife_Ats_Block</class>
            </ats>
        </blocks>
        <helpers>
            <ats>
                <class>Easylife_Ats_Helper</class>
            </ats>
        </helpers>
        <resources>
            <ats_setup>
                <setup>
                    <module>Easylife_Ats</module>
                </setup>
            </ats_setup>
        </resources>
        <events>
          <checkout_type_onepage_save_order>
                <observers>
                    <ats>
                        <type>singleton</type>
                        <class>ats/observer</class>
                        <method>saveCustomData</method>
                    </ats>
                </observers>
            </checkout_type_onepage_save_order>

        </events>
    </global>
</config>

Ats/Model/Observer.php

<?php

class Easylife_Ats_Model_Observer
{

    public function saveCustomData(Varien_Event $observer)
    {
        $event = $observer->getEvent();
        $order = $event->getOrder();
        $fieldVal = Mage::app()->getFrontController()->getRequest()->getParams();
        Mage::log($fieldVal);
        $order->setDeliveryDate($fieldVal['delivery_date']);
    }
}

Ats/sql/ats_setup/installer-0.1.0.php

<?php

/* @var $installer Mage_Core_Model_Resource_Setup */
require_once('app/Mage.php');

$installer = $this;

$installer->startSetup();

Mage::app()->setCurrentStore(Mage::getModel('core/store')->load(Mage_Core_Model_App::ADMIN_STORE_ID));
$installer = new Mage_Sales_Model_Resource_Setup('core_setup');

$attribute  = array(
    'type' => 'varchar',
    'backend_type' => 'varchar',
    'frontend_input' => 'varchar',
    'is_user_defined' => true,
    'label' => 'Delivery Date',
    'visible' => true,
    'required' => false,
    'user_defined' => false,
    'default' => '0',
    'comparable' => false,
    'searchable' => false,
    'filterable' => false
);

$installer->addAttribute('order','delivery_date',$attribute);
$installer->addAttribute('quote','delivery_date',$attribute);

$installer->endSetup();

design\frontend\base\default\template\checkout\onepage\shipping_method.phtml

<div id="onepage-checkout-shipping-method-additional-load">
        <?php echo $this->getChildHtml('additional') ?>
    </div>
    <div>
        <input id="delivery_date" name="delivery_date" value="" class="input-text" type="text">

design\adminhtml\default\default\template\sales\order\view\info.phtml

<?php if($_order->getDeliveryDate()): ?>
                    <tr>
                        <td class="label"><label><?php echo Mage::helper('sales')->__('Delivery Date') ?></label></td>
                        <td class="value"><strong><?php echo $_order->getDeliveryDate(); ?></strong></td>
                    </tr>
                <?php endif; ?>

Can you tell me where I went wrong?