Fix Android rescheduled notifications firing immediately

Fix Android rescheduled notifications firing immediately, ref: https://github.com/invertase/react-native-firebase/pull/1035/files

Safe FirebaseMessaging usage

Update README.md

Changing the default version to fetch latest available version online.

Updating the build.gradle guideline for using latest versions of framework.
Revert the filename of icon suggested in README

Removing the useless note line.

Huge update for Android setup.

Update README.md

upgrade versions of android target, compile sdk and support-core-utils

New line is just important....

Add back the `+` to the line.

Adding common steps for a successful installation.
Adding `Pod 'Firebase` as the required step for Pod installation.
Adding common troubleshooting steps.

delete notification channel method

Separates versioning for firebase-core and firebase-messaging.  These…

separates versioning for firebase-core and firebase-messaging.  These are no longer coupled in recent releases by Google.

Group alert behavior

add channel

Fixed processDebugGoogleServices building error

1. Move the google-services plugin to the bottom to avoid a building time error
2. Error message: app:processDebugGoogleServices FAILED

Fix notification grouping