luke-chang/gaia — pull request #52 by dwi2 (2014-03-26 14:30:57+00:00)
Title: 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’
}
```