refactor(item): changed notes from a class to an element

Closes #251

ionic/components/item/item.ts

@@ -14,9 +14,9 @@ import {dom} from 'ionic/util';
  * <ion-list>
  *   <ion-item *ng-for="#item of items" (click)="itemTapped($event, item)">
  *     {{item.title}}
- *     <div class="item-note" item-right>
+ *     <ion-note item-right>
  *       {{item.note}}
- *     </div>
+ *     </ion-note>
  *   </ion-item>
  * </ion-list>
  *  ```

ionic/components/item/modes/ios.scss

@@ -134,7 +134,7 @@ $item-ios-divider-padding:            5px 15px !default;
     margin-bottom: 1px;
   }
 
-  .item-note {
+  ion-note {
     color: $item-ios-note-color;
   }
 

ionic/components/item/modes/md.scss

@@ -137,7 +137,7 @@ $item-md-divider-padding:            5px 15px !default;
     line-height: $item-md-body-text-line-height;
   }
 
-  .item-note {
+  ion-note {
     color: $item-md-note-color;
   }