network, web_service: Add Verification backend and use new lobby API

Added verify_backend to load user_data for members. and removed method to generate UID as this is now done server-side.

Added GetUsername function and a "token" param to room_member.
Also added a username to ChatEntry, so that the username can be shown (along with nicknames) in the chat dialog.

src/network/verify_user.h

@@ -0,0 +1,45 @@
+// Copyright 2018 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <string>
+#include "common/logging/log.h"
+
+namespace Network::VerifyUser {
+
+struct UserData {
+    std::string username;
+    std::string display_name;
+    std::string avatar_url;
+};
+
+/**
+ * A backend used for verifying users and loading user data.
+ */
+class Backend {
+public:
+    virtual ~Backend();
+
+    /**
+     * Verifies the given token and loads the information into a UserData struct.
+     * @param verify_UID A GUID that may be used for verification.
+     * @param token A token that contains user data and verification data. The format and content is
+     * decided by backends.
+     */
+    virtual UserData LoadUserData(const std::string& verify_UID, const std::string& token) = 0;
+};
+
+/**
+ * A null backend where the token is ignored.
+ * No verification is performed here and the function returns an empty UserData.
+ */
+class NullBackend final : public Backend {
+public:
+    ~NullBackend();
+
+    UserData LoadUserData(const std::string& verify_UID, const std::string& token) override;
+};
+
+} // namespace Network::VerifyUser