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.
Using a nodeIterator might make this function slightly cleaner and tidier. At the moment with all the early returns it's quite tricky to keep track of what's happening. 

See https://developer.mozilla.org/en/docs/Web/API/NodeIterator for more