🇸🇪Sweden @deadbeef

@ptmkenny If it's ok with @SiarheiNik I will refactor using config as soon as I get time and try to keep the interface as close to the legacy module as possible. We just needed this to work like yesterday with our credentials policy.

Another thing to discuss is whether typing the various Android/iOS bits and pieces adds enough value. The message itself is a simple, well-documented JSON string and just building it and sending it is very easy to just template, rather than instantiating loads of objects to later then just simply render it out anyway.

Here's an update which fixes among other things:

• Allows Google credentials path to be set in the environment through $_ENV or otherwise ( credentials files inside the webroot aren't really desirable ).
• Fixes sendToTopic() to use the condition field if topics field is not set
• Fixes the jsonSerialize function declaration of FCMOptions to return array and avoid warning
• Misc coding standards fixes.