fix(ngInclude): correctly add non-html namespaced template content

It is now possible for ngInclude to correctly load SVG content in non-blink
browsers, which do not sort out the namespace when parsing HTML.

/CC @tbosch / @IgorMinar

Closes #7538
Can you debug this a little more to find out why they don't have a parent / when they are added to the parent? I don't like having this comment in the source :-)