quickfix to delegate svg/root to the html watcher like canvas

[joshuafcole]

• Enables using html.addExternalRoot() to control SVG placement
• Enables mixing SVG into html documents, a feature I'd embarrassingly forgotten that the previous SVG library lacked.
• This fix is robust, but the original DOM library abstraction is really creaking here, it's worth revisiting in the future. This is especially the case since UI performance can be easily improved by an order of magnitude or more by not mirroring the instances back into Eve. In 0.4, this isn't really an issue, but 0.3 could really benefit from the boost.