Add client-side navigation support for wp-ignore directive

[DAreRodz]

What

Allows elements with the wp-ignore directive to keep their content after navigate calls.

Why

During navigations, the content inside elements with wp-ignore could change, and those updates should not be reflected (those parts of the HTML document should be ignored).

How

Implementing the ignore directive in a way that:

1. its content it's not parsed.
2. the value for the dangerouslySetInnerHTML prop never changes.

[luisherranz]

I like it 🙂