Halloheadings plugin rewrite

Hi 

Ive rewritten the halloheading plugin to make better use of the button widget and make it work in IE (current one doesn't work in IE at all).

Tested In: 
- Chrome 23
- Safari 6
- IE 8
- IE 7

I will be looking at some other plugins for IE compatibility over the next few days. 

Thanks for all your hard work, what a great little editor it is.