Added partial Android FCM support (#975)

* Modified plugin.xml to include FCM changes

* Plugin.xml changes for FCM

* Java changes for FCM

* Increased plugin version to 2.0.0

* Increased plugin version in package.json

* Added topic subscription/unsubscription

* Removed some empty lines

plugin.xml

@@ -96,4 +96,4 @@
       <preference name="WindowsToastCapable" value="true"/>
     </config-file>
   </platform>
-</plugin>
+</plugin>

src/android/com/adobe/phonegap/push/PushPlugin.java

@@ -346,7 +346,10 @@ private void subscribeToTopics(JSONArray topics, String registrationToken) {
             String topic = null;
             for (int i=0; i<topics.length(); i++) {
                 topic = topics.optString(i, null);
-                subscribeToTopic(topic, registrationToken);
+                if (topic != null) {
+                    Log.d(LOG_TAG, "Subscribing to topic: " + topic);
+                    FirebaseMessaging.getInstance().subscribeToTopic(topic);
+                }
             }
         }
     }
@@ -364,6 +367,10 @@ private void unsubscribeFromTopics(JSONArray topics, String registrationToken) {
             for (int i=0; i<topics.length(); i++) {
                 topic = topics.optString(i, null);
                 unsubscribeFromTopic(topic, registrationToken);
+                if (topic != null) {
+                    Log.d(LOG_TAG, "Unsubscribing to topic: " + topic);
+                    FirebaseMessaging.getInstance().unsubscribeFromTopic(topic);
+                }
             }
         }
     }