Support for receiving "canonical id" update events from pushserver.

// FREEBIE

src/main/java/org/whispersystems/textsecuregcm/entities/UnregisteredEvent.java

@@ -11,6 +11,9 @@ public class UnregisteredEvent {
   @NotEmpty
   private String registrationId;
 
+  @JsonProperty
+  private String canonicalId;
+
   @JsonProperty
   @NotEmpty
   private String number;
@@ -26,6 +29,10 @@ public class UnregisteredEvent {
     return registrationId;
   }
 
+  public String getCanonicalId() {
+    return canonicalId;
+  }
+
   public String getNumber() {
     return number;
   }

src/main/java/org/whispersystems/textsecuregcm/push/FeedbackHandler.java

@@ -76,7 +76,13 @@ public class FeedbackHandler implements Managed, Runnable {
               event.getTimestamp() > device.get().getPushTimestamp())
           {
             logger.info("GCM Unregister Timestamp matches!");
-            device.get().setGcmId(null);
+
+            if (event.getCanonicalId() != null && !event.getCanonicalId().isEmpty()) {
+              logger.info("It's a canonical ID update...");
+              device.get().setGcmId(event.getCanonicalId());
+            } else {
+              device.get().setGcmId(null);
+            }
             accountsManager.update(account.get());
           }
         }