center cursor directly in Menu class

centering in Screen::Scroll is hacky and works
only for scrolling, not e.g. selecting.

src/outputs.cpp

@@ -35,6 +35,7 @@ void Outputs::Init()
 {
 	w = new Menu<MPD::Output>(0, MainStartY, COLS, MainHeight, "", Config.main_color, brNone);
 	w->CyclicScrolling(Config.use_cyclic_scrolling);
+	w->CenteredCursor(Config.centered_cursor);
 	w->HighlightColor(Config.main_highlight_color);
 	w->SetItemDisplayer(Display::Pairs);