Need functions to set priority

[tardypad]

We've updated the libcapn library recently on our servers from 1.0.0 to 1.1.0 and experienced the issue that notifications are not received properly by the devices.
From some tests, notifications are received only if the application is already open on the foreground.
After further investigations, I've found out that the issue is caused by a behavior change in the 1.1.0 release with the new priorities function (adobkin/libcapn@5c666af)
The default priority is set to "default" which cause the notifications not to be sent immediately (but by batch later or maybe never)
Unfortunately those new functions are not accessible from the php wrapper module, so we can't currently adapt the priority for devices to receive notifications immediately as before.
If this field was not sent in the previous version, the notification was considered to have high priority
https://developer.apple.com/library/ios/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/Chapters/APNsProviderAPI.html