/// <summary>
/// Remove screen from the manager.
/// </summary>
/// <param name="a"></param>
public static void removeScreen(Screen a)
{
_screens.Remove(a.getName());
}
/// <summary>
/// Adds the screen to the manager.
/// </summary>
/// <param name="a"></param>
public static void addScreen(Screen a)
{
_screens.Add(a.getName(), a);
}