Display embedded SVG images in the PDF export

HTML5 allows to simply mix HTML and SVG elements in a document, making it easier to include vector graphics in a page. Although XWiki doesn't have yet a dedicated macro which would allow to include some SVG content in a wiki document, it is possible to do so by abusing the html macro. The problem is that when trying to export the document as PDF, only the textual content of the SVG is displayed as inline text. There's a very simple fix for this, since FOP already supports rendering SVG images.