feat(graphs.graph) add xmlns attributes to svg

I want to export glimpse.js svg graphs to images but to do this the
xml must be valid. To make valid xml it requries specifying the xmlns attributes.
Look here for more info: https://github.com/mbostock/d3/issues/1935
Merge pull request #219 from racker/add_xmlns_attributes_to_svg_render

Add xmlns attributes to svg and defs elements