Windows specific refactoring of Mouse3DController and RemovableDriveManager.

PrusaSlicer newly registers by Windows operating system for HID USB
plug / unplug notifications and for Volume attach / detach notifications,
and the background threads of the two respective services are waken up
on these Windows notifications.
The RemovableDriveManager also wakes up every 30 seconds to cope with
the drives ejected from Windows Explorer or from another application,
for example Cura, for which Windows OS does not send out notifications.

src/slic3r/GUI/RemovableDriveManager.hpp

@@ -84,6 +84,11 @@ public:
 	// It would be better to make this method private and friend to RemovableDriveManagerMM, but RemovableDriveManagerMM is an ObjectiveC class.
 	void 		update();
 
+#ifdef _WIN32
+    // Called by Win32 Volume arrived / detached callback.
+	void 		volumes_changed();
+#endif // _WIN32
+
 private:
 	bool 			 		m_initialized { false };
 	wxEvtHandler*			m_callback_evt_handler { nullptr };
@@ -95,6 +100,9 @@ private:
 	std::condition_variable m_thread_stop_condition;
 	mutable std::mutex 		m_thread_stop_mutex;
 	bool 					m_stop { false };
+#ifdef _WIN32
+    std::atomic<bool>		m_wakeup { false };
+#endif /* _WIN32 */
 #endif // REMOVABLE_DRIVE_MANAGER_OS_CALLBACKS
 
 	// Called from update() to enumerate removable drives.
@@ -114,10 +122,7 @@ private:
 	// Set with set_and_verify_last_save_path() to a removable drive path to be ejected.
 	std::string 			m_last_save_path;
 
-#if _WIN32
-	//registers for notifications by creating invisible window
-	//void register_window_msw();
-#elif __APPLE__
+#if __APPLE__
     void register_window_osx();
     void unregister_window_osx();
     void list_devices(std::vector<DriveData> &out) const;