added firebase and rudimentary leaderboard support

addons/godot-firebase/auth/providers/google.gd

@@ -0,0 +1,13 @@
+class_name GoogleProvider
+extends AuthProvider
+
+func _init(client_id: String,client_secret: String):
+	set_client_id(client_id)
+	set_client_secret(client_secret)
+	self.should_exchange = true
+	self.redirect_uri = "https://accounts.google.com/o/oauth2/v2/auth?"
+	self.access_token_uri = "https://oauth2.googleapis.com/token"
+	self.provider_id = "google.com"
+	self.params.response_type = "code"
+	self.params.scope = "email openid profile"
+	self.params.response_type = "code"