Added favicon; changed rewrite conditions

Something very strange happened when I added a favicon; the css broke
on the site and stayed broken even when I reverted all my changes.  I
am not really sure what happened (or why this delay occurred) but
seemingly the cause is that the overgeneralized rewrite condition
interacts badly with the css loading (as well as svg elements like the
glyph icons).  This is the recommended fix but not a fully general
solution—if there are other filetypes code igniter is doing exciting
behind the scenes stuff with we should just keep our eyes peeled for a
problem there.