Qt: Add translation support (#664)

* Translation PoC

* i18n but better

* More Greek translation

* Add proper translation UI

* Linux CI: Install qt6-tools-dev

include/panda_qt/main_window.hpp

@@ -126,6 +126,7 @@ class MainWindow : public QMainWindow {
 	void setupControllerSensors(SDL_GameController* controller);
 	void sendMessage(const EmulatorMessage& message);
 	void dispatchMessage(const EmulatorMessage& message);
+	void loadTranslation();
 
 	// Tracks whether we are using an OpenGL-backed renderer or a Vulkan-backed renderer
 	bool usingGL = false;