Add feedback handler.

// FREEBIE

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

@@ -0,0 +1,33 @@
+package org.whispersystems.textsecuregcm.entities;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import org.hibernate.validator.constraints.NotEmpty;
+
+import javax.validation.constraints.Min;
+
+public class UnregisteredEvent {
+
+  @JsonProperty
+  @NotEmpty
+  private String registrationId;
+
+  @JsonProperty
+  @NotEmpty
+  private String number;
+
+  @JsonProperty
+  @Min(1)
+  private int deviceId;
+
+  public String getRegistrationId() {
+    return registrationId;
+  }
+
+  public String getNumber() {
+    return number;
+  }
+
+  public int getDeviceId() {
+    return deviceId;
+  }
+}

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

@@ -0,0 +1,17 @@
+package org.whispersystems.textsecuregcm.entities;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+import java.util.LinkedList;
+import java.util.List;
+
+public class UnregisteredEventList {
+
+  @JsonProperty
+  private List<UnregisteredEvent> devices;
+
+  public List<UnregisteredEvent> getDevices() {
+    if (devices == null) return new LinkedList<>();
+    else                 return devices;
+  }
+}