[shimgvw] Add icons for different images

Currently, shimgvw has one icon for the 4 major picture types. This patch adds new icons for the different image types.

bmp.ico is from the Gnome Icon Theme and is released under the GNU General Public License version 2 License
https://commons.wikimedia.org/wiki/GNOME_Desktop_icons#/media/File:Gnome-image-x-generic.svg

png.ico is from the Tango Icon Theme
https://commons.wikimedia.org/wiki/Tango_icons#/media/File:Image-x-generic-2.svg