Plugin update for newer Openfire and APNS versions

[nsobadzhiev]

Hi guys!

I was implementing push notifications for Openfire. I used this plugin and updated it to work with newer Openfire versions and I also switched to using Pushy for sending the actual pushes.

It its core, the plugin is similar to this one, but I already modified many things. I could open a PR and you might consider accepting these changes, but granted, they are sometimes opinionated and might not be what you are going for in this project.

Anyway, any feedback is appreciated so let me know what you think. You can find my code here.