EogScrollView: Use better downscaling filter to fix Bug 665897

Replace all instances of CAIRO_FILTER_BILINEAR with CAIRO_FILTER_GOOD.
This produces much less aliasing on downscaled images. CAIRO_FILTER_GOOD
uses the same method as CAIRO_FILTER_BILINEAR for scale factors greater
than 0.75, according to https://bugs.webkit.org/show_bug.cgi?id=147826.

Comparison screenshots made with eog 3.18.1: http://imgur.com/a/NaoOs

CAIRO_FILTER_BEST is better still, but the the visual difference is
almost imperceptible and the performance impact is severe.

https://bugzilla.gnome.org/show_bug.cgi?id=665897