GH-3012 add --offline and --name arguments

These allow launching offline with a specified name from the command line.

launcher/Application.h

@@ -154,7 +154,8 @@ public slots:
         bool online = true,
         BaseProfilerFactory *profiler = nullptr,
         MinecraftServerTargetPtr serverToJoin = nullptr,
-        MinecraftAccountPtr accountToUse = nullptr
+        MinecraftAccountPtr accountToUse = nullptr,
+        const QString &offlineName = QString()
     );
     bool kill(InstancePtr instance);
 
@@ -234,6 +235,8 @@ public:
     QString m_instanceIdToLaunch;
     QString m_serverToJoin;
     QString m_profileToUse;
+    bool m_offline = false;
+    QString m_offlineName;
     bool m_liveCheck = false;
     QUrl m_zipToImport;
     std::unique_ptr<QFile> logFile;