This makes them discoverable in dconf-editor.

Modify inverted colors preference to fall back to GSettings when no
per-document metadata exists. This allows users to set inverted colors
as the default preference, which will apply to all documents that don't
have an explicit per-document preference.

Fixes #710

EPUB files with missing or incomplete metadata (like no title or missing
navigation elements) can cause NULL pointer dereferences in the XML
parsing functions. This adds NULL checks to xml_parse_children_of_node,
get_child_list, and the TOC text parsing loop.

Fixes #707

Adds a new --reset-metadata command-line option that clears all stored
metadata (page position, zoom level, window geometry, etc.) for
specified document files before opening them. This allows users to open
documents with a fresh state, ignoring any previously remembered
settings.

Change the caja extension feature option to default to 'auto' instead of
'enabled', so that atril builds on systems without libcaja-extension.

Fixes #673

Backported from https://gitlab.gnome.org/GNOME/evince/-/commit/021428c9

Check that the content file exists before attempting to parse it, and
handle failures in document title extraction gracefully.