The names of the icons are in the WEB-INF/classes/icons.properties file.
If you want to change them, copy the icons.properties file to custom-icons.properties and then add the line IconsFile=custom-icons.properties to your configuration.properties file. By doing this, you do not have to worry about a future upgrade overwriting the icons, or the icon list file.
Finally, edit the custom-icons.properties file, replacing the names of the default icons with the names of the icons you want to use.