Add ValueResourceLoader that has <item ... type="layout"> to PackageResourceLoader

For multi pane layout, I used layout.xml

### res/values/layout.xml
```
<?xml version="1.0" encoding="utf-8"?>
<resources>
    <item name="main_layout" type="layout">@layout/activity_main</item>
    <bool name="has_two_panes">false</bool>
</resources>
```

### res/values/layout.xml
```
<?xml version="1.0" encoding="utf-8"?>
<resources>
    <item name="main_layout" type="layout">@layout/activity_main_land</item>
    <bool name="has_two_panes">true</bool>
</resources>
```

### MainActivity.java
```
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main_layout);

    initView();
    initMainFragment();
}
```

Robolectric could not parse <item type="layout"> of <resources>.