Re-render block with current context

[dmarcelino]

This PR comes out of necessity. I needed to re-use a block but I needed to translate into a different language, hence it needed to be rendered again.

Changes:

• saves BlockNodeProxy to context instead of saving the render result
• when rendering SameNode it re-renders BlockNodeProxy using the current context

I believe this provides greater flexibility to sameas since it can reuse a block in dynamic fashion, so to speak.