Core/PacketsIO: Updated and enabled SMSG_CHANNEL_NOTIFY, CMSG_CHAT_REGISTER_ADDON_PREFIXES, CMSG_CHAT_UNREGISTER_ALL_ADDON_PREFIXES

- Thanks to @MitchesD for all his help, you're awesome!
- Packets have been sniffed & parsed and they all check out.

src/server/game/Server/Packets/ChatPackets.cpp

@@ -233,3 +233,15 @@ WorldPacket const* WorldPackets::Chat::ChatServerMessage::Write()
 
     return &_worldPacket;
 }
+
+void WorldPackets::Chat::ChatRegisterAddonPrefixes::Read()
+{
+    int32 count;
+    _worldPacket >> count;
+
+    for (int32 i = 0; i < count; ++i)
+    {
+        uint32 lenghts = _worldPacket.ReadBits(5);
+        Prefixes.push_back(_worldPacket.ReadString(lenghts));
+    }
+}