Relax new line detection

An empty new line test should return true when there is an
empty bold, italic or other inline style but with no 
meaningful text.

This pull request improves the test such that empty non-block
elements are considered newlines.
I'm not sure how we would check for the kind of structure we are looking for. We are asserting that we have a set of purely nested inline elements with no forks in the tree and a leaf that is <br> or ''. The NodeIterator doesn't provide anyway to infer structure.

Perhaps as you suggest later, we relax it even further and just assert that we only have inline elements with no text content in which case it is trivial to use NodeIterator.