Changes to HTML output and indentation

- Writing a tag now checks the avoidWhitespace() method before the opening tag.
- A newline + indentation is written before the closing /tag if any of the childnodes created a newline (avoidWhitespace() == false).
- instead of calling the indent()-method and then deciding to indent or not, now we check first and then call the method or we don't. (saves the creation of a StringBuilder and one append-operation)
- removed the overridden avoidWhitespace() method from <title> elements

it's still not perfect, but i think it fails in fewer cases than the previous solution.

the check (subNode instanceof DOMElement) is rather ugly. it is the quick way of doing it. I could have also changed the render-method to return the desired information, but that would have been a bit extensive. (or one could move the avoidWhitespace method to DOMNode)