updatexlrator.cgi: Update to naming of variables in css section
- This updates the updatexlrator.cgi page to the same central use of extraHead from
header.pl and simplifying of css variables where appropriate.
- The variables for the percentage bar will also be able to be used in other cgi pages
with a percent bar.
Tested-by: Adolf Belka <adolf.belka@ipfire.org> Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>