private void buttonBack_LeftMouseClickedCallback(object sender, CallbackArgs e)
{
this.GUI.Get<Button>("buttonBack").Visible = false;
this.GUI.Get<Button>("buttonSendRegistration").Visible = false;
this.GUI.Get<Button>("buttonSendLogin").Visible = false;
this.GUI.Get<EditBox>("textUser").Visible = false;
this.GUI.Get<EditBox>("textPassword").Visible = false;
this.GUI.Get<Label>("labelUsername").Visible = false;
this.GUI.Get<Label>("labelPassword").Visible = false;
this.GUI.Get<Label>("labelNews").Visible = true;
this.GUI.Get<Button>("buttonLogin").Visible = true;
this.GUI.Get<Button>("buttonRegistration").Visible = true;
}