updatexlrator.cgi: Fixes bug#13024 - Table style rendering bug

updatexlrator.cgi: Fixes bug#13024 - Table style rendering bug

- This is happening due to the use of bgcolor which has been deprecated since HTML4.01 and
   is no longer supported in HTML5
- Similar approach used here as was used in the same fix for the dhcp.cgi page
- CSS based approach utilised.
- Partially tested in my vm testbed. The percentage bar works withg no problems.
   The table could not be confirmed as in my testbed I don't have updatexlrator running
   as my updates are all based on https and not http.
- The table will need to be confirmed by the bug reporter or someone else that uses
   updatexlrator

Fixes: Bug#13024
Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>