Make Notification Factory cache certificates, or make the factory implement an interface

[stevenmyhre]

I get "bad password" errors when I send multiple notifications in the same process - using a new message builder for each one, creating a new certificate for each (via Notificato::createCertificate method). Simple solution was to cache the certificate objects so they can be used again. But it would be nice if the CertificateFactory supported this. It only caches a default one. I'd like to key the cache off of the pem location. Was going to implement my own CertificateFactory for this, but turns out the setCertificateFactory typehints to the concrete implementation of Apns\CertificateFactory. I can make my own factory and use it outside the scope of this library, but thought I would recommend it to the repo... sorry, no time for PRs!

[mac-cain13]

Agreed, nice idea! I don't have the time and incentive to implement this right now. But leave it open until somebody has the time to implement this in the library.

Note that I myself never have seen the "bad password" error even sending hundreds of notifications. So that is a bit strange, would like to know if more people see this problem.