Templated index.html file for supporting error pages.

grunt-templtated-index-with-errorpages.html

<div class="page-container">
    <div class="site-content">
        <!-- build:remove:error400,error404 -->
        <div ui-view="mainBody"></div>
        <!-- /build -->
        <!-- build:include:error400 error/400.html --><!-- /build-->
        <!-- build:include:error404 error/404.html --><!-- /build-->
    </div>
</div>