Add gtkimageview at 1.3.0. While there is a newer version, gdt has

Add gtkimageview at 1.3.0.  While there is a newer version, gdt has
been using this version with ufraw, and is therefore committing it
before upgrading.

GtkImageView is a simple image viewer widget for GTK. Similar to the
image viewer panes in gThumb or Eye of Gnome. It makes writing image
viewing and editing applications easy. Among its features are:

    * Mouse and keyboard zooming.
    * Scrolling and dragging.
    * Adjustable interpolation.
    * Fullscreen mode.
    * GIF animation support.