graphics/pqiv: Update to 2.13.2

• Move USES to a better place (portlint).
• Convert the BACKENDS option GROUP to MULTI as pqiv needs at least one backend to compile.
• Enable more formats by default to make the package more useful. LIBARCHIVE, LIBAV (for video), POPPLER (for PDF) and WEBP were added to the list. In the Debian package, whose pqiv developer is the package maintainer, all the backends seem to be enabled by default.
• Default to GTK3. This is the default in the Debian package too.
• Update pkg-descr according to the current README.markdown from the upstream project.

Changelog: https://github.com/phillipberndt/pqiv/releases/tag/2.13.2