[WIP] Support touch scroll in register

Just as an experiment, I'd like to compare how standard scrolling
behavior feels in the register view.  I find the current fast and
quantized scroll to be disconcerting, but I recognize that a lot of
thought, and trial and error, have already gone into the existing
custom scroll interactions.

This patch replaces custom scrolling with a ScrolledWindow container,
but is incomplete in many ways:
* Breaks mouse wheel scrolling.
* Breaks cursor scrolling (with keyboard).

However, I like some of what we get:
* Touch interaction feels correct.
* Fading scrollbars are more modern and consistent.

gnucash/register/register-gnome/gnucash-register.c

@@ -521,7 +521,6 @@ gnucash_register_create_widget (Table *table)
     GtkWidget *header;
     GtkWidget *widget;
     GtkWidget *sheet;
-    GtkWidget *scrollbar;
 
     reg = g_object_new (GNUCASH_TYPE_REGISTER, NULL);
     widget = GTK_WIDGET(reg);
@@ -538,41 +537,31 @@ gnucash_register_create_widget (Table *table)
     gtk_widget_set_vexpand (header, FALSE);
     gtk_widget_set_valign (header, GTK_ALIGN_FILL);
     g_object_set (header, "margin", 0, NULL);
-    gtk_widget_show (header);
-
-    gtk_grid_attach (GTK_GRID(widget), sheet, 0, 1, 1, 1);
-    gtk_widget_set_hexpand (sheet, TRUE);
-    gtk_widget_set_halign (sheet, GTK_ALIGN_FILL);
-    gtk_widget_set_vexpand (sheet, TRUE);
-    gtk_widget_set_valign (sheet, GTK_ALIGN_FILL);
-    g_object_set (sheet, "margin", 0, NULL);
-    gtk_widget_show (sheet);
-
-    scrollbar = gtk_scrollbar_new (GTK_ORIENTATION_VERTICAL, GNUCASH_SHEET(sheet)->vadj);
-    gtk_grid_attach (GTK_GRID(widget), GTK_WIDGET(scrollbar), 1, 0, 1, 2);
-    gtk_widget_set_hexpand (GTK_WIDGET(scrollbar), FALSE);
-    gtk_widget_set_halign (GTK_WIDGET(scrollbar), GTK_ALIGN_FILL);
-    gtk_widget_set_vexpand (GTK_WIDGET(scrollbar), TRUE);
-    gtk_widget_set_valign (GTK_WIDGET(scrollbar), GTK_ALIGN_FILL);
-    g_object_set (GTK_WIDGET(scrollbar), "margin", 0, NULL);
-    gtk_widget_show (scrollbar);
-    GNUCASH_SHEET(sheet)->vscrollbar = scrollbar;
-
-    scrollbar = gtk_scrollbar_new (GTK_ORIENTATION_HORIZONTAL, GNUCASH_SHEET(sheet)->hadj);
-    gtk_grid_attach (GTK_GRID(widget), GTK_WIDGET(scrollbar), 0, 2, 1, 1);
-    gtk_widget_set_hexpand (GTK_WIDGET(scrollbar), TRUE);
-    gtk_widget_set_halign (GTK_WIDGET(scrollbar), GTK_ALIGN_FILL);
-    gtk_widget_set_vexpand (GTK_WIDGET(scrollbar), FALSE);
-    gtk_widget_set_valign (GTK_WIDGET(scrollbar), GTK_ALIGN_FILL);
-    g_object_set (GTK_WIDGET(scrollbar), "margin", 0, NULL);
-    reg->hscrollbar = scrollbar;
-    gtk_widget_show (reg->hscrollbar);
-    reg->hscrollbar_visible = TRUE;
-    GNUCASH_SHEET(sheet)->hscrollbar = scrollbar;
+
+    GtkWidget* swin =
+        GTK_WIDGET(gtk_scrolled_window_new (NULL, NULL));
+    gtk_scrolled_window_set_policy (GTK_SCROLLED_WINDOW(swin),
+                                    GTK_POLICY_AUTOMATIC,
+                                    GTK_POLICY_AUTOMATIC);
+    GNUCASH_SHEET(sheet)->vscrollbar =
+        gtk_scrolled_window_get_vscrollbar(GTK_SCROLLED_WINDOW(swin));
+    GNUCASH_SHEET(sheet)->hscrollbar =
+        gtk_scrolled_window_get_hscrollbar(GTK_SCROLLED_WINDOW(swin));
 
     g_signal_connect (GNUCASH_SHEET(sheet)->hadj, "changed",
                       G_CALLBACK (gnucash_register_update_hadjustment), reg);
 
+    gtk_container_add (GTK_CONTAINER(swin), GTK_WIDGET(sheet));
+
+    gtk_grid_attach (GTK_GRID(widget), swin, 0, 1, 1, 1);
+    gtk_widget_set_hexpand (swin, TRUE);
+    gtk_widget_set_halign (swin, GTK_ALIGN_FILL);
+    gtk_widget_set_vexpand (swin, TRUE);
+    gtk_widget_set_valign (swin, GTK_ALIGN_FILL);
+    g_object_set (swin, "margin", 0, NULL);
+
+    gtk_widget_show_all (widget);
+
     return widget;
 }