move new tab button into the tabs start widget

src/app/browser/window/header/bar/append/widget.rs

@@ -1,35 +0,0 @@
-use gtk::{
-    gio::SimpleAction,
-    prelude::{ActionExt, ButtonExt},
-    Align, Button,
-};
-use std::sync::Arc;
-
-pub struct Widget {
-    gobject: Button,
-}
-
-impl Widget {
-    // Construct
-    pub fn new_arc(action_tab_append: SimpleAction) -> Arc<Self> {
-        // Init gobject
-        let gobject = Button::builder()
-            .icon_name("tab-new-symbolic")
-            .css_classes(["flat"])
-            .valign(Align::Center)
-            .tooltip_text("New tab")
-            .build();
-
-        // Init events
-        gobject.connect_clicked(move |_| {
-            action_tab_append.activate(None);
-        });
-
-        Arc::new(Self { gobject })
-    }
-
-    // Getters
-    pub fn gobject(&self) -> &Button {
-        &self.gobject
-    }
-}