Added support for 'line-no-highlight' class

Added the 'line-no-highlight' class to lines that are within an embed containing highlighting, making it possible to specifically style non-highlighted lines. The class doesn't apply to embeds that have no highlighting.
I can't maintain this within my IDE. The auto-formatting options in PHPStorm are simply *have a space* or *don't have a space* within brackets – there is no condition based on whether or not the content of brackets will be a variable, so I can never really accurately follow that particular piece of Wordpress coding standards. I'm wrong either way.

I'm just using the PHPStorm config settings maintained by Rarst - https://gist.github.com/Rarst/1370155