use modern (2018) pattern for modules

src/browser/header/tray/mod.rs

@@ -1,33 +0,0 @@
-mod menu;
-mod tab;
-
-use gtk::prelude::BoxExt;
-use gtk::{Box, Orientation};
-use menu::Menu;
-use tab::Tab;
-
-pub struct Tray {
-    widget: Box,
-}
-
-impl Tray {
-    pub fn new() -> Self {
-        let menu = Menu::new();
-        let tab = Tab::new();
-
-        let widget = Box::builder()
-            .orientation(Orientation::Horizontal)
-            .spacing(8)
-            .build();
-
-        widget.append(menu.widget());
-        widget.append(tab.widget());
-
-        Self { widget }
-    }
-
-    // Getters
-    pub fn widget(&self) -> &Box {
-        &self.widget
-    }
-}