CSS region folding

See [Discussion](https://groups.google.com/forum/#!topic/ace-discuss/JkeDqTJAUso)

This pull request includes both CSS and Javascript region folding, which includes all of the changes in my [Javascript region folding pull reuqest] (https://github.com/ajaxorg/ace/pull/2238). 

The Javascript region folding does not change any existing behavior except for added region folding support.

However, the CSS region folding has to change the behavior for it to work properly. The changed behavior is that single line comments in CSS  no longer render a fold widget unless they are region start comments: /*#region [optional description]*/