Add `badge` argument to `client.Client.publish_to_ios` method

[Ernesto González]

From Local and Remote Notification Programming Guide: Creating the Remote Notification Payload, we see that the "aps" entry includes a "badge" entry itself, which accepts an integer to set the app's devices badge number.

We'll had an optional badge argument to client.Client.publish_to_ios in order to be able to pass a payload like

{
    "aps" : {
        "alert" : {
            "title" : string,
            "body" : string,
            "sound": string
        },
        "badge" : number
    },
    "id" : string,
    "type": string,
    "serializer": object
}

In order to pass badge down to publish_to_ios we nee to add the badge param to the following methods:

• tasks.send_sns_mobile_push_notification_to_device
• models.Device.send
• and finally client.Client.publish_to_ios.