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.
This has nothing to do with space over tabs, but has everything to do with the size of tabs I'm using – will change on next commit. 

Also, the $no_highlight variable is being set in there because it only applies when an embed has highlighting. I'll move it so it it simpler to understand.