Supports specifying the root container, not just document.body #550
Description
Users should be able to specify a particular container (such as .v-application) either through configuration or programmatically, where all guide elements generated by Driver.js will be placed, rather than being appended to the document.body.
<body>
<div class="v-application">
<!-- content -->
<!-- generate by driver.js -->
<!-- CSS ".m-application red { }" will work -->
<div id="driver-popover-content red"></div>
<svg class="driver-overlay"></svg>
</div>
</body>