Add support to load into remote views.

Closes https://github.com/square/picasso/issues/14

@JakeWharton 

Proposed APIs:
```java
public void into(RemoteViews remoteViews, int viewId, int[] appWidgetIds)
public void into(RemoteViews remoteViews, int viewId, int notificationId, Notification notification)
```

- Support for `RemoteViews` on notifications and widgets. Placeholder and error are also supported.

![device-2014-02-07-175236](https://f.cloud.github.com/assets/310370/2115985/bd20f864-9063-11e3-9fe3-e10add421fac.png)