Reimplementation of Dialogs

Cleanup code to integrate multithreading process for dialogs into the DialogToolkit (avoid poluting UserInterfaceManager and improves reliability)

UserInterfaceManager.h

@@ -12,6 +12,7 @@
 
 #include "SourceList.h"
 #include "InfoVisitor.h"
+#include "DialogToolkit.h"
 
 struct ImVec2;
 class MediaPlayer;
@@ -183,6 +184,11 @@ class UserInterface
     FrameGrabber *webcam_emulator_;
 #endif
 
+    // Dialogs
+    DialogToolkit::OpenSessionDialog *sessionopendialog;
+    DialogToolkit::OpenSessionDialog *sessionimportdialog;
+    DialogToolkit::SaveSessionDialog *sessionsavedialog;
+
     // Private Constructor
     UserInterface();
     UserInterface(UserInterface const& copy) = delete;