Support minimize and maximize state.

Fixes #6893.  Minimize is mostly useful for tooling, and maximize is a
more user-friendly way of specifying a fullscreen shortcut.

Windows/MainWindow.cpp

@@ -360,6 +360,10 @@ namespace MainWindow
 		}
 	}
 
+	void Minimize() {
+		ShowWindow(hwndMain, SW_MINIMIZE);
+	}
+
 	RECT DetermineWindowRectangle() {
 		RECT rc;