switch to simpler way of themeing PNG icons

main.go

@@ -27,11 +27,11 @@ func main() {
 	}
 
 	fyneApp := app.New()
-	fyneApp.Settings().SetTheme(&theme.MyTheme{
-		NormalFont: myApp.Config.Application.FontNormalTTF,
-		BoldFont:   myApp.Config.Application.FontBoldTTF,
-		Config:     &myApp.Config.Theme,
-	})
+	theme := theme.NewMyTheme(&myApp.Config.Theme)
+	theme.NormalFont = myApp.Config.Application.FontNormalTTF
+	theme.BoldFont = myApp.Config.Application.FontBoldTTF
+	fyneApp.Settings().SetTheme(theme)
+	
 	w := float32(myApp.Config.Application.WindowWidth)
 	if w <= 1 {
 		w = 1000