Account: Fix column index in load_filters
gdk-pixbuf vapi: Update to newest version

Also, add a variadic argument to save_to_stream to unbreak the bindings.
tests/media: Add aniamtion download test
Utils: Add write_pixbuf_async function

Since write_to_stream_async is broken, we need to work around that.
InlineMediaDownloader: Port to write_pixbuf_async
Utils: Remove old extern pixbuf constructors

Since we rely on a new valac version anyways, we can also make use of
async constructors.