Change GIF icons to use a different palette, for more smoothness.

Updating powered-by images to reflect the consensus on dev@ ML. Please do review and say if this is what we want, and I'll backport if so.

Updating the 'powered by' icons to both say 2.4 as well as use Apache 2.0 licensed fonts only. SVG version also added, in case someone wants to use/change/reproduce the icons.

merge r358287: Update 'apache_pb2' images for Apache-2.2 (NOTE: not for 2.3!)

A couple of new options for sysadmins. Still waiting on opinions between replacing the image on docroot/index.html.* with 2.0, or 2.0 animated.