Make VQmod XML file work with different themes

[kevinb456]

Currently the VQmod XML file used to edit the footer template is hard-coded to edit the default template footer file;

<file name="catalog/view/theme/default/template/common/footer.tpl">
        <operation>
            <search position="before" offset="1"><![CDATA[</body>]]></search>
            <add><![CDATA[
<?php echo $piwik_footer_text; ?>
            ]]></add>
        </operation>
</file>

If a custom template is used, this will not make the modifications correctly.

[kevinb456]

Fixed #2 in commit d987221.