fix the welcome window not being closeable

due to the chat being in front of it,
by giving the welcome window a depth of -1.0.
The value of -1.0 is very arbitrary, but has some effect on
further development*, so there should be consideration concerning it.

* if something is supposed to be over/under the welcome window and
over/under something else with a different depth at the same time,
the resulting depth could become really ugly.
Of course it's always possible to change depths afterwards, but this often
breaks things, so the general scope of depths should
imo be considered, before this becomes a problem.

voxygen/src/hud/mod.rs

@@ -662,6 +662,7 @@ impl Hud {
                 Intro::Show => {
                     Rectangle::fill_with([800.0, 850.0], Color::Rgba(0.0, 0.0, 0.0, 0.80))
                         .mid_left_with_margin_on(ui_widgets.window, 10.0)
+                        .depth(-1.0)
                         .set(self.ids.intro_bg, ui_widgets);
                     Text::new(intro_text)
                         .top_left_with_margins_on(self.ids.intro_bg, 10.0, 10.0)