reorganize widget modules

src/browser/header/tray/tab/mod.rs

@@ -1,19 +1,23 @@
-mod widget;
+use gtk::Button;
 
 pub struct Tab {
-    pub widget: widget::Tab,
+    pub widget: Button,
 }
 
 impl Tab {
     // Construct
     pub fn new() -> Tab {
         Self {
-            widget: widget::Tab::new(),
+            widget: Button::builder()
+                .action_name("win.tab_append")
+                .icon_name("tab-new-symbolic")
+                .tooltip_text("New tab")
+                .build(),
         }
     }
 
     // Getters
-    pub fn widget(&self) -> &widget::Tab {
+    pub fn widget(&self) -> &Button {
         &self.widget
     }
 }