Open presets from a menu at the foot of the tool rail

Presets were a "Presets…" button in develop's top bar that opened a
sheet over the photograph, so applying one was two clicks with the
picture covered. They are now an entry pinned to the bottom of the tool
rail, apart from the tools because a preset arms nothing, and it opens a
menu beside the rail: the same sectioned rows the sheet lists, one click
to apply to the open photograph. The menu's last row, "Save or manage…",
opens the sheet, which keeps saving, renaming, reverting and importing,
since those take a name or a path.

The menu is a PopupWindow for the film list's reasons, with the list in
a clipped box of its own; the Flickable alone let its last row draw over
the manage row. Choosing from it zeroes preset-apply-count before
applying, since the grid may have left its selection count there.

The manual says where presets are now and gains a picture of the open
menu. The scenes reach the sheet through the menu and aim the manage
row from the rail's entry, as the film list's rows are aimed, because
the automation reports a popup's elements in the popup's coordinates.

ui/dr-ui/src/presets.rs

@@ -1000,8 +1000,8 @@ pub fn wire_named(
 
     // --- opening the sheet over the open photograph -----------------------
     //
-    // The develop column's "Presets…" button, and everything opening the sheet
-    // from there means. It used to be four lines inside the panel's
+    // "Save or manage…" in the tool rail's presets menu, and everything
+    // opening the sheet from there means. It used to be four lines inside the panel's
     // instantiation in `app.slint`, which is exactly the sort of behaviour a
     // second drawing of that panel would have had to copy; `Transfer` is a
     // global and a global cannot bind the window's own state, so it lands