Magento – Adjust Columns width/size in Product Grid in Magento Admin

The qty field comes from the template file app/design/adminhtml/default/default/template/catalog/product/tab/inventory.phtml

    <tr>
        <td class="label"><label for="inventory_qty"><?php echo Mage::helper('catalog')->__('Qty') ?><span class="required">*</span></label></td>
        <td class="value">
            <?php if (!$_readonly):?>
            <input type="hidden" id="original_inventory_qty" name="<?php echo $this->getFieldSuffix() ?>[stock_data][original_inventory_qty]" value="<?php echo $this->getFieldValue('qty')*1 ?>"/>
            <?php endif;?>
            <input type="text" class="input-text required-entry validate-number" id="inventory_qty" name="<?php echo $this->getFieldSuffix() ?>[stock_data][qty]" value="<?php echo $this->getFieldValue('qty')*1 ?>" <?php echo $_readonly;?>/>
        </td>
        <td class="value scope-label"><?php echo Mage::helper('adminhtml')->__('[GLOBAL]') ?></td>
    </tr>

You can change your admin theme and add your own template

This should be adminhtml below routers and not configsliders in your config.xml.

<admin>
    <routers>
        <adminhtml>                               
            <args>
                <modules>
                    <Namespace_Configslider after="Mage_Adminhtml">Namespace_Configslider_Adminhtml</Namespace_Configslider>
                </modules>                                
            </args>
        </adminhtml>
   </routers>
</admin>

Also, I'd recommend this guide.

http://alanstorm.com/magento_admin_hello_world_revisited

Updated answer based on new info.

Without re-creating the entire module, this is what I changed to get the admin page to show up and not 404. I substituted the namespace for my testing so you will need to change that. You should be able to take it from here.

Pay close attention to the order of the namespace_extensionname in the config edits, these are important.

Modified: app/etc/local/Stackexchange/Configslider/etc/config.xml

<?xml version="1.0" encoding="UTF-8"?>
<config>
    <modules>
        <Stackexchange_Configslider>
            <version>0.1.0</version>
        </Stackexchange_Configslider>
    </modules>

    <global>
        <helpers>
            <stackexchange_configslider>
                <class>Stackexchange_Configslider_Helper</class>
            </stackexchange_configslider>
        </helpers>

        <blocks>
            <configslider>
                <class>Namespace_Configslider_Adminhtml_Block</class>
            </configslider>
        </blocks>
    </global>

    <admin>
        <routers>
            <adminhtml>
                <args>
                    <modules>
                        <Stackexchange_Configslider after="Mage_Adminhtml">Stackexchange_Configslider_Adminhtml</Stackexchange_Configslider>
                    </modules>
                </args>
            </adminhtml>
        </routers>
    </admin>

    <adminhtml>
        <layout>
            <updates>
                <stackexchange_configslider module="stackexchange_configslider">
                    <file>stackexchange_configslider.xml</file>
                </stackexchange_configslider>
            </updates>
        </layout>
    </adminhtml>
</config>

Modified: app/etc/local/Stackexchange/Configslider/etc/adminhtml.xml

<?xml version="1.0"?>
<config>
    <menu>
        <cms>
            <children>
                <stackexchange translate="title" module="stackexchange_configslider">
                    <title>Configure the slider</title>
                    <sort_order>50</sort_order>
                    <action>adminhtml/configslider/index</action>
                </stackexchange>
            </children>
        </cms>
    </menu>

    <acl>
        <resources>
            <admin>
                <children>
                    <cms>
                        <children>
                            <stackexchange translate="title" module="stackexchange_configslider">
                                <title>Configure the slider</title>
                                <sort_order>100</sort_order>
                            </stackexchange>
                        </children>
                    </cms>
                </children>
            </admin>
        </resources>
    </acl>
</config>

Missing: app/etc/local/Stackexchange/Configslider/controllers/Adminhtml/ConfigsliderController.php

<?php

class Stackexchange_Configslider_Adminhtml_ConfigsliderController extends Mage_Adminhtml_Controller_Action
{
    public function indexAction()
    {
        $this->loadLayout();
        $this->renderLayout();
    }
}