Switch to GCM CCS and add support for APN feedback processing.

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

@@ -55,10 +55,6 @@ public class EncryptedOutgoingMessage {
     this.serialized = Base64.encodeBytes(ciphertext);
   }
 
-  public EncryptedOutgoingMessage(String serialized) {
-    this.serialized = serialized;
-  }
-
   public String serialize() {
     return serialized;
   }

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

@@ -0,0 +1,51 @@
+package org.whispersystems.textsecuregcm.entities;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+public class PendingMessage {
+
+  @JsonProperty
+  private String sender;
+
+  @JsonProperty
+  private long   messageId;
+
+  @JsonProperty
+  private String encryptedOutgoingMessage;
+
+  public PendingMessage() {}
+
+  public PendingMessage(String sender, long messageId, String encryptedOutgoingMessage) {
+    this.sender                    = sender;
+    this.messageId                 = messageId;
+    this.encryptedOutgoingMessage  = encryptedOutgoingMessage;
+  }
+
+  public String getEncryptedOutgoingMessage() {
+    return encryptedOutgoingMessage;
+  }
+
+  public long getMessageId() {
+    return messageId;
+  }
+
+  public String getSender() {
+    return sender;
+  }
+
+  @Override
+  public boolean equals(Object other) {
+    if (other == null || !(other instanceof PendingMessage)) return false;
+    PendingMessage that = (PendingMessage)other;
+
+    return
+        this.sender.equals(that.sender) &&
+        this.messageId == that.messageId &&
+        this.encryptedOutgoingMessage.equals(that.encryptedOutgoingMessage);
+  }
+
+  @Override
+  public int hashCode() {
+    return this.sender.hashCode() ^ (int)this.messageId ^ this.encryptedOutgoingMessage.hashCode();
+  }
+}