gitweb: Do not use absolute font sizes

gitweb: Do not use absolute font sizes

Avoid specifying font sizes in pixels, since that is just pure evil.
Pointed out by Chris Riddoch.

Note that this is pretty much just a proposal; I didn't test if everything
fits perfectly right, but things seem to be pretty much okay. repo.or.cz
uses it now as a test drive - if you find any visual quirks, please point
them out, with a patch if possible since I'm total CSS noob and debugging
CSS is an extremely painful experience for me.

Note that this patch actually does change visual look of gitweb in Firefox
with my resolution and default settings - everything is bigger and I can't
explain the joy of actually seeing gitweb text that is in _readable_ size;
also, my horizontal screen real estate feels better used now. But judging
from the look of most modern webpages on the 'net, most people prefer
reading the web with strained eyes and/or a magnifying glass (I wonder what
species of scientists should look into this mystifying phenomenon) - so,
please tell us what you think.

Maybe we might want to get rid of absolute sizes other than font sizes in
the CSS file too in the long term.

Signed-off-by: Petr Baudis <pasky@suse.cz>
Signed-off-by: Junio C Hamano <junkio@cox.net>