use canonical module subfolder tree

src/browser/main/tab/page/mod.rs

@@ -0,0 +1,16 @@
+mod content;
+mod navigation;
+
+use gtk::prelude::BoxExt;
+use gtk::Box;
+
+pub fn new() -> Box {
+    let page = Box::builder()
+        .orientation(gtk::Orientation::Vertical)
+        .build();
+
+    page.append(&navigation::new());
+    page.append(&content::new());
+
+    page
+}