[PATCH] icons upgrade

This updates the icons from the current anthony-*.gif series to the
completely free PNG silk icons by Mark James.

Why?
  * Avoiding GIF format makes Squid just a little bit more FOSS than before.

  * These icons are also just a little bit smaller and slicker.

  * Distros which package the silk icons separately for other apps can
leverage those packages and share the icons.

Also moves the icons to /var/www/squid/icons in accordance with the
filesystem specs for static web content.

votes? opinions?

Amos