Tidy up "firewall_nat_out.php" XHTML

Close BR, INPUT and IMG tags and ALT to IMG tags
Update HTML Boolean operators
Move NOWRAP to class statement
Move CENTER tag to ALIGN statement in TD tag
Add missing closing SPAN tag
Add missing closing P tag
Merge pull request #615 from ExolonDX/branch_07

Tidy up "firewall_nat_out.php" XHTML