Fixed types that are now obsolete (#204)

Author: vchelaru

articles/tutorials/building_2d_games/21_customizing_gum_ui/snippets/titlescene/usings.cs

@@ -5,7 +5,7 @@
 using Microsoft.Xna.Framework.Graphics;
 using Microsoft.Xna.Framework.Input;
 using MonoGameGum;
-using MonoGameGum.Forms.Controls;
+using Gum.Forms.Controls;
 using MonoGameGum.GueDeriving;
 using MonoGameLibrary;
 using MonoGameLibrary.Graphics;

articles/tutorials/building_2d_games/23_completing_the_game/snippets/gamesceneui/definition.cs

@@ -5,7 +5,7 @@
 using Microsoft.Xna.Framework.Audio;
 using Microsoft.Xna.Framework.Content;
 using MonoGameGum;
-using MonoGameGum.Forms.Controls;
+using Gum.Forms.Controls;
 using MonoGameGum.GueDeriving;
 using MonoGameLibrary;
 using MonoGameLibrary.Graphics;