SingleTileImageryProvider crossing 180 degrees longitude does not render

I'm guessing this is a more general problem than with just `SingleTileImageryProvider`, but it's the easiest way to reproduce the issue.

**Sandcastle example**

``` javascript
var viewer = new Cesium.Viewer('cesiumContainer', {
baseLayerPicker : false
});

viewer.scene.imageryLayers.addImageryProvider(new Cesium.SingleTileImageryProvider({
url : '../images/Cesium_Logo_Color.jpg',
rectangle : Cesium.Rectangle.fromDegrees(160, 60, -160, 78)
}));

viewer.entities.add({
polyline : {
positions : Cesium.Cartesian3.fromDegreesArray([-180, 80,
-180, 20]),
width : 1
}
});
```

Start by running the Sandcastle example from the issue with SingleTileImageryProvider and the rectangle crossing 180 degrees. Trace how the provider handles the Rectangle and antimeridian during imagery rendering. Done means the image renders across the specified 160 to -160 degree range, with a regression check for this example.

Written by the indexing model from the issue text.