Fix issue #43, respond with callback instead of event in systemConnection

**IMPORTANT**
**不再使用`system-action-object`事件通知response回傳內容**

systemConnection各function變更signature如下
```javascript
    addWidget(args, callback)
    removeWidget(args, callback)
    updateWidget(args, callback)
    showAll(callback)
    hideAll(callback)
```
callback的signature必須如下
```javascript
function callback(messageObject)
```
成功時messageObject
```json
      {
        requestId: ‘87548a9b-3e64-4aca-9366-f4856e5f7a65’,
        action: 'add',
        result: true,
        widgetId: ‘widget-idY’
      }
```
失敗時
```json
      {
        requestId: ‘87548a9b-3e64-4aca-9366-f4856e5f7a65’,
        action: 'add',
        result: false,
        errorCause: ‘timeout’
      }
```