Use fillColor and strokeColor instead of fillStyle and strokeStyle

The color names are more intuitive.  And if we want to support pattern strokes or fills, we'll need additional proerties to represent other pattern properties.

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

@@ -15,7 +15,7 @@ describe('ol.style.Style', function() {
             symbolizers: [
               new ol.style.Shape({
                 size: 4,
-                fillStyle: '#BADA55'
+                fillColor: '#BADA55'
               })
             ]
           })
@@ -24,7 +24,7 @@ describe('ol.style.Style', function() {
       var feature = new ol.Feature();
       feature.set('foo', 'bar');
       expect(style.apply(feature).length).toBe(1);
-      expect(style.apply(feature)[0].fillStyle).toBe('#BADA55');
+      expect(style.apply(feature)[0].fillColor).toBe('#BADA55');
       feature.set('foo', 'baz');
       expect(style.apply(feature).length).toBe(0);
     });