UI: Add fullscreen projector to systray menu

(Edit by Jim: Changed it to just add the fullscreen projector sub-menu
like when right-clicking the preview, that way it doesn't have to add
new locale text for translators, and allows the users to specify which
monitor to use)

Closes jp9000/obs-studio#845

UI/window-basic-main.cpp

@@ -5396,8 +5396,13 @@ void OBSBasic::SystemTrayInit()
 	connect(exit, SIGNAL(triggered()),
 			this, SLOT(close()));
 
+	QMenu *previewProjector = new QMenu(QTStr("PreviewProjector"));
+	AddProjectorMenuMonitors(previewProjector, this,
+			SLOT(OpenPreviewProjector()));
+
 	trayMenu = new QMenu;
 	trayMenu->addAction(showHide);
+	trayMenu->addMenu(previewProjector);
 	trayMenu->addAction(sysTrayStream);
 	trayMenu->addAction(sysTrayRecord);
 	trayMenu->addAction(sysTrayReplayBuffer);