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/line.test.js

@@ -7,16 +7,16 @@ describe('ol.style.LineLiteral', function() {
     it('identifies equal literals', function() {
       var literal = new ol.style.LineLiteral({
         strokeWidth: 3,
-        strokeStyle: '#BADA55',
+        strokeColor: '#BADA55',
         opacity: 1
       });
       var equalLiteral = new ol.style.LineLiteral({
-        strokeStyle: '#BADA55',
+        strokeColor: '#BADA55',
         strokeWidth: 3,
         opacity: 1
       });
       var differentLiteral = new ol.style.LineLiteral({
-        strokeStyle: '#013',
+        strokeColor: '#013',
         strokeWidth: 3,
         opacity: 1
       });
@@ -34,7 +34,7 @@ describe('ol.style.Line', function() {
 
     it('accepts literal values', function() {
       var symbolizer = new ol.style.Line({
-        strokeStyle: '#BADA55',
+        strokeColor: '#BADA55',
         strokeWidth: 3
       });
       expect(symbolizer).toBeA(ol.style.Line);