Tidy up "system_gateway_groups.php" XHTML

Close INPUT and IMG tags and add alt to IMG tags
Move TFOOT between THEAD and TBODY, this is a "quirck" of HTML
Move NOWRAP to class
Deprecate ampersand in ANCHOR tags
Add dummy row to TBODY otherwise it will generate and error if there are
now groups.
Merge pull request #529 from ExolonDX/branch_23

Tidy up "system_gateway_groups.php" XHTML