Add Firebase (FCM) support

[avencat]

This PR adds Firebase support to this repository. I'm not an Android developer so please feel free to let me know if there's some weirdness on the code. I made this PR as GCM is being outdated and need to be replaced by FCM. In order to do this PR, I followed the steps provided by @Rah1x in #697. Hope this will help!

[calcazar]

I'm supporting a clone of this library located here: https://github.com/calcazar/react-native-push-notification-CE and added your changes to it :)

[iamarkdev]

@zo0r - Can we get this reviewed?

[baselbj]

so is it now supporting firebase?

[alexsegura]

Also see #710 for changes in AndroidManifest.xml

EDIT: Oh ok I didn't see that you documented it 👍

[lucidtheory]

Been a few months and no word. Does this need to be forked to use these changes?

may just use the fork @calcazar built. Thanks

[alexsegura]

Personally, I switched to using react-native-firebase for Android 😐

[Gp2mv3]

@zo0r has no more time to manage this repo. He gave me the access. What's the state of this PR ? Is it ready to be merged according to you ? Do you have a working example of it ?

[avencat]

Hi @Gp2mv3 yes I think it’s ready, I’ll give it a check tomorrow, you can check this fork that already uses it: https://github.com/calcazar/react-native-push-notification-CE

[avencat]

@Gp2mv3 that's ok, I checked! :)