Generating your own GCM Push Notification Key
1.1 Create a project at https://console.developers.google.com/project for your app.
1.2 Select your Project and go to IAM & admin->Settings. Your project number should be located on this page.
Copy the "Project Number" from this page.
You will need to add it to the source code of your app later when you follow the SDK guide.
3.1 Under "APIs & services" > "Credentials", click "Create credentials".
3.3 Press the "Create" button.
DO NOT enter anything into the box.
3.4 Go to https://console.firebase.google.com and import your google project
4.1 Send your Project Number(Sender ID) and GCM Server key to email@example.com.