ui/app,apps/gophers,apps/hello: replace CreateWindow with NewWindow

Gio doesn't support multiple windows anyway, so get rid of the
app.Windows channel and use NewWindow call for the mobile platforms
as well.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

apps/gophers/main.go

@@ -119,14 +119,6 @@ func main() {
 		fmt.Println("The quota for anonymous GitHub API access is very low. Specify a token with -token to avoid quota errors.")
 		fmt.Println("See https://help.github.com/en/articles/creating-a-personal-access-token-for-the-command-line.")
 	}
-	err := app.CreateWindow(app.WindowOptions{
-		Width:  ui.Dp(400),
-		Height: ui.Dp(800),
-		Title:  "Gophers",
-	})
-	if err != nil {
-		log.Fatal(err)
-	}
 	app.Main()
 }
 
@@ -147,13 +139,16 @@ func init() {
 	fonts.italic = mustLoadFont(goitalic.TTF)
 	fonts.mono = mustLoadFont(gomono.TTF)
 	go func() {
-		for w := range app.Windows() {
-			w := w
-			go func() {
-				if err := newApp(w).run(); err != nil {
-					log.Fatal(err)
-				}
-			}()
+		w, err := app.NewWindow(app.WindowOptions{
+			Width:  ui.Dp(400),
+			Height: ui.Dp(800),
+			Title:  "Gophers",
+		})
+		if err != nil {
+			log.Fatal(err)
+		}
+		if err := newApp(w).run(); err != nil {
+			log.Fatal(err)
 		}
 	}()
 }