Add empty page offering download

data/ui/empty_page.blp

@@ -0,0 +1,72 @@
+using Gtk 4.0;
+using Adw 1;
+
+template $MusicusEmptyPage: Adw.NavigationPage {
+  title: _("New Library");
+
+  Adw.ToolbarView {
+    [top]
+    Adw.HeaderBar header_bar {
+      [end]
+      MenuButton {
+        icon-name: "open-menu-symbolic";
+        menu-model: primary_menu;
+      }
+    }
+
+    Adw.StatusPage {
+      icon-name: "library-symbolic";
+      title: _("New Library");
+      description: _("You can import your recordings by selecting \"Import music\" in the main menu. Musicus also comes with a small pre-made library of recordings. You can download it using the button below.");
+
+      child: Gtk.Box {
+        orientation: vertical;
+
+        Gtk.Button download_button {
+          halign: center;
+          label: _("Download music");
+          clicked => $download_library() swapped;
+
+          styles [
+            "suggested-action",
+            "pill",
+          ]
+        }
+
+        Adw.Clamp {
+          Gtk.ListBox process_list {
+            selection-mode: none;
+            margin-top: 12;
+            visible: false;
+
+            styles [
+              "boxed-list-separate",
+            ]
+          }
+        }
+      };
+    }
+  }
+}
+
+menu primary_menu {
+  item {
+    label: _("_Import music");
+    action: "win.import";
+  }
+
+  item {
+    label: _("_Library manager");
+    action: "win.library";
+  }
+
+  item {
+    label: _("_Preferences");
+    action: "win.preferences";
+  }
+
+  item {
+    label: _("_About Musicus");
+    action: "app.about";
+  }
+}