Update vaadin-combo-box to 1.0.0-alpha4, add vaadin-icons.

bower.json

@@ -25,7 +25,8 @@
   ],
   "dependencies": {
     "vaadin-grid": "vaadin/vaadin-grid#~1.0.0",
-    "vaadin-combo-box": "vaadin/vaadin-combo-box#1.0.0-alpha3"
+    "vaadin-combo-box": "vaadin/vaadin-combo-box#1.0.0-alpha4",
+    "vaadin-icons": "vaadin/vaadin-icons#master"
   },
   "devDependencies": {
     "iron-component-page": "polymerelements/iron-component-page#~1.1.0",