Allow push notifications on Android Oreo (#952)

* Handle channelId if specified

With Android Oreo it is necessary to specify a channel id when
sending out push notifications. This will check if such an
id is specified and in case it is available it will be set
on notification before it is being built

* Upgrade compile/build for Oreo

With Android Oreo it's necessary to specify a
channelId for push notifications to be handled.

This will bump gradle to allow for using those new methods

packages/aws-amplify-react-native/android/build.gradle

@@ -22,8 +22,8 @@ allprojects {
 apply plugin: "com.android.library"
 
 android {
-    compileSdkVersion 23
-    buildToolsVersion "23.0.1"
+    compileSdkVersion 26
+    buildToolsVersion "26.0.1"
 
     defaultConfig {
         minSdkVersion 16

packages/aws-amplify-react-native/android/src/main/java/com/amazonaws/amplify/pushnotification/modules/RNPushNotificationHelper.java

@@ -153,7 +153,7 @@ public void sendToNotificationCentre(Bundle bundle) {
                 if (msg == null) {
                     // this happens when a 'data' notification is received - we do not synthesize a local notification in this case
                     Log.d(LOG_TAG, "Cannot send to notification centre because there is no 'message' field in: " + bundle);
-                    return;   
+                    return;
                 }
             }
 
@@ -289,6 +289,13 @@ public void sendToNotificationCentre(Bundle bundle) {
                 }
             }
 
+            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+                String channelId = bundle.getString("android_channel_id");
+                if (channelId != null) {
+                    notification.setChannelId(channelId);
+                }
+            }
+
             int notificationID = Integer.parseInt(notificationIdString);
 
             PendingIntent pendingIntent = PendingIntent.getActivity(context, notificationID, intent,