use canonical module subfolder tree

src/browser/main/mod.rs

@@ -0,0 +1,14 @@
+mod tab;
+
+use gtk::prelude::BoxExt;
+use gtk::Box;
+
+pub fn new() -> Box {
+    let main = Box::builder()
+        .orientation(gtk::Orientation::Vertical)
+        .build();
+
+    main.append(&tab::new());
+
+    main
+}