SVG support for metal-views

This greatly improves SVG support in metal-view by basing the current namespace off the contextual element. SVG components like `{{somePath` should be viable with this change.

TODO

* [ ] Make some demo JSBins to test this visually, SVG can be tricky
* [ ] Confirm it in a real app

/cc @bantic @heyjinkim blesh for you all to try out, if you please.