Multiple style class support

Hey mate,

I added support for multiple style class values (as in CSS) and updated the sorting order of the selectors so that the last one (on cad file) overwrites the previously declared one. I am not sure what my implications my changes in the styleItem: method will have as your previously traversed the style nodes in reverse order.

I did not update the parser to support selectors with multiple classes (like CSS: .style1.style2) but it works fine if you declare just multiple selectors.

Please let me think what you think about that.

Cheers,

Alex


Changelog:

- added support for multiple style_class values by assigning a string which can contain whitespace separated values
- changed the sorting of the style selectors by precedence so that it matches the order in the cas file (would match more the behaviour of the CSS standard)
- changed styling order of items to traverse style nodes from top to bottom order instead of reverse