Add ng-scope and ng-binding classes to CSS classes documentation page

I noticed angular was adding these css classes to elements and believe they should be listed in the documentation at this page. The ng-scope class is mentioned in the developer guide, hence the link there, and the ng-binding class is not mentioned anywhere else in the documentation or the guide that I found.
docs(css_styling_guide): add ng-scope and ng-binding classes

I noticed angular was adding these css classes to elements and believe they
should be listed in the documentation at this page. The ng-scope class is
mentioned in the developer guide, hence the link there, and the ng-binding
class is not mentioned anywhere else in the documentation or the guide that
I found.

Closes #3728