Css facet doesn't handle absence of a property set on the higher level data object

[jasoniangreen]

Add a test for empty object into the Css_test.js file and you'll see it fails.

it('should delete all classes when data is set to null/undefined', function() {
        testWith(null);
        testWith(undefined);
        testWith({}); <-- this one fails

This also opens up a bigger question about iterating css classes config, rather than data, to determine what needs to be changed. We also had questions about the use of dots being appended to data properties. We can talk about it with @Richard-Walton when he's back.