Bug 7500 - Use CSS Sprites for faster page loading

Bug 7500 - Use CSS Sprites for faster page loading

This patch moves *most* small interface icons and
the Koha log into a single 10K sprite image. CSS
is used to position the sprite correctly for each
icon instance.

Not covered by this patch: XSLT icons, star ratings
icons, table sort icons (the latter which I don't
think can be done using this technique).

A follow-up patch should remove the individual images
which have been replaced by the sprite.

Signed-off-by: Dobrica Pavlinusic <dpavlin@rot13.org>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>