Treating geometry as just another attribute

The first set geometry is considered the default.  As an added bonus, we're back to a single argument constructor.  Later, we could allow a schema to be set.  This would be done before setting values (calling constructor with no args).

test/spec/ol/style/shape.test.js

@@ -30,7 +30,7 @@ describe('ol.style.Shape', function() {
         opacity: new ol.Expression('opacityAttr')
       });
 
-      var feature = new ol.Feature(undefined, {
+      var feature = new ol.Feature({
         sizeAttr: 42,
         opacityAttr: 0.4
       });