review d3node field in pod

[jonyrock]

So Pod has protected readonly d3Node which is the root html element we insert <svg> tag.
I believe that d3Node should wrap <svg> tag, not it's parent.

[jonyrock]

The right field now to use is Pod.svg which we remove on each "rendering".
It's all connected with idea to place each pod in a separate <g> element

[jonyrock]

This issue will not be actual if we remove d3-related code from the core