Refactoring visibility related events

1. remove unnecessary events from MainViewModel
2. remove usage of Obsolete api (show, hide etc)
3. fix space problem in #660
4. part of #486
5. fix up/down key bug introduced in 92b7ca6a1bafd254e39ee92812ff691906cd85c1
6. fix #678

Plugins/Wox.Plugin.Sys/Main.cs

@@ -161,7 +161,7 @@ namespace Wox.Plugin.Sys
                     IcoPath = "Images\\app.png",
                     Action = c =>
                     {
-                        context.API.CloseApp();
+                        Application.Current.MainWindow.Close();
                         return true;
                     }
                 },