Add portable lock feature

If the file "portable.txt" is present in the application directory,
MO will force itself to be launched as a portable instance.  The
change game button and menu item are hidden to prevent the user
from changing out of the portable instance.

src/instancemanager.cpp

@@ -186,6 +186,10 @@ QString InstanceManager::queryInstanceName(const QStringList &instanceList) cons
 
 QString InstanceManager::chooseInstance(const QStringList &instanceList) const
 {
+  if (portableInstallIsLocked()) {
+    return QString();
+  }
+
   enum class Special : uint8_t {
     NewInstance,
     Portable,
@@ -266,6 +270,19 @@ bool InstanceManager::portableInstall() const
 }
 
 
+bool InstanceManager::portableInstallIsLocked() const
+{
+  return QFile::exists(qApp->applicationDirPath() + "/" +
+                       QString::fromStdWString(AppConfig::portableLockFileName()));
+}
+
+
+bool InstanceManager::allowedToChangeInstance() const
+{
+  return !portableInstallIsLocked();
+}
+
+
 void InstanceManager::createDataPath(const QString &dataPath) const
 {
   if (!QDir(dataPath).exists()) {
@@ -286,6 +303,10 @@ void InstanceManager::createDataPath(const QString &dataPath) const
 QString InstanceManager::determineDataPath()
 {
   QString instanceId = currentInstance();
+  if (portableInstallIsLocked()) 
+  {
+    instanceId.clear();
+  }
   if (instanceId.isEmpty() && !m_Reset && (m_overrideInstance || portableInstall()))
   {
     // startup, apparently using portable mode before

src/instancemanager.h

@@ -38,6 +38,8 @@ class InstanceManager {
 
   QString currentInstance() const;
 
+  bool allowedToChangeInstance() const;
+
 private:
 
   InstanceManager();
@@ -58,6 +60,7 @@ class InstanceManager {
 
   void createDataPath(const QString &dataPath) const;
   bool portableInstall() const;
+  bool portableInstallIsLocked() const;
 
 private:
 

src/mainwindow.cpp

@@ -727,6 +727,10 @@ void MainWindow::setupToolbar()
   } else {
     log::warn("no separator found on the toolbar, icons won't be right-aligned");
   }
+
+  if (!InstanceManager::instance().allowedToChangeInstance()) {
+    ui->actionChange_Game->setVisible(false);
+  }
 }
 
 void MainWindow::setupActionMenu(QAction* a)

src/shared/appconfig.inc

@@ -17,6 +17,7 @@ APPPARAM(std::wstring, proxyDLLOrig, L"steam_api_orig.dll") // needs to be ident
 APPPARAM(std::wstring, proxyDLLSource, L"proxy.dll")
 APPPARAM(std::wstring, vfs32DLLName, L"usvfs_x86.dll")
 APPPARAM(std::wstring, vfs64DLLName, L"usvfs_x64.dll")
+APPPARAM(std::wstring, portableLockFileName, L"portable.txt")
 APPPARAM(const wchar_t*, localSavePlaceholder, L"__MOProfileSave__\\")
 
 APPPARAM(std::wstring, firstStepsTutorial, L"tutorial_firststeps_main.js")