Re-record the manual on the 0.16.0 interface

Every scene was recorded again on a release build of this commit with
the automation feature. Master changed what nearly every picture shows
after they were taken: scrollbars on the develop column, the grid, the
sidebar and Settings; a "?" beside Settings in develop's top bar, with
its controls regrouped; the Film row opening its list as a popup.

The film scene pressed the list's rows through the develop column, which
no longer holds them: the list is a popup, and the automation hook
reports its contents relative to it. The scene now opens it with
film_list_open, turns the wheel down it and back so the popup and its
scrollbar are seen scrolling, and clicks Velvia at its popup position
plus the popup's origin. The caption says so. film_reach passed in the
same run: the last stock was reached by the wheel, a drag, the scrollbar
and the keys.

Looked at as contact sheets of each GIF's middle and last frames and
each PNG. launch, launch-folder, library-nesting.png and
library-collection-menu came out byte-identical after optipng and are
unchanged. develop-zoom's deepest frames are smooth on Xvfb as before;
its caption does not claim blocks. Settings shows version 0.15.0,
the build's own, until the release commit bumps it.

docs/manual/README.md

@@ -251,7 +251,7 @@ sensor does not. The list opens over the column and scrolls on its own — by
 wheel, drag or flick, or with `Up`, `Down` and `Enter` — down to the
 black-and-white stocks at its end.
 
-![Choosing Velvia, then holding Before](media/film.gif)
+![Opening the film list, scrolling it, choosing Velvia, then holding Before](media/film.gif)
 
 ### History, snapshots, presets
 

docs/manual/index.html

@@ -312,7 +312,7 @@ named stock; below it, the print exposure and push controls a film has and a
 sensor does not. The list opens over the column and scrolls on its own — by
 wheel, drag or flick, or with <code>Up</code>, <code>Down</code> and <code>Enter</code> — down to the
 black-and-white stocks at its end.</p>
-<figure><img loading="lazy" src="media/film.gif" alt="Choosing Velvia, then holding Before"><figcaption>Choosing Velvia, then holding Before</figcaption></figure>
+<figure><img loading="lazy" src="media/film.gif" alt="Opening the film list, scrolling it, choosing Velvia, then holding Before"><figcaption>Opening the film list, scrolling it, choosing Velvia, then holding Before</figcaption></figure>
 <h3 id="history-snapshots-presets">History, snapshots, presets</h3>
 <p>Every change is a step; <code>Undo</code> and the History panel walk them. <code>Snapshot</code>
 keeps the current state under a name. <code>Presets…</code> saves the settings to