Refactor the friend namespace (#721)

* Refactor the friend namespace and UInt128

This commit also:
- Fix GetFriendsList arguments ordering.
- Add GetFriendListIds.
- Expose the permission level of the port instance.
- InvalidUUID => InvalidArgument

* friend: add all cmds as commments

* add Friend structure layout

* Rename FriendErr to FriendError

* Accurately implement INotificationService

* Fix singleton lock of NotificationEventHandler

* Address comments

* Add comments for IDaemonSuspendSessionService cmds

* Explicitly define the Charset when needed

Also make "Nickname" a string

* Address gdk's comments

Ryujinx.HLE/HOS/Services/FspSrv/IFileSystemProxy.cs

@@ -1,6 +1,7 @@
 using LibHac;
 using LibHac.Fs;
 using LibHac.Fs.NcaUtils;
+using Ryujinx.Common;
 using Ryujinx.Common.Logging;
 using Ryujinx.HLE.FileSystem;
 using Ryujinx.HLE.HOS.Ipc;
@@ -234,9 +235,7 @@ namespace Ryujinx.HLE.HOS.Services.FspSrv
 
             long titleId = context.RequestData.ReadInt64();
 
-            UInt128 userId = new UInt128(
-                context.RequestData.ReadInt64(), 
-                context.RequestData.ReadInt64());
+            UInt128 userId = context.RequestData.ReadStruct<UInt128>();
 
             long            saveId       = context.RequestData.ReadInt64();
             SaveDataType    saveDataType = (SaveDataType)context.RequestData.ReadByte();