Tidy up "system_firmware_check.php" XHTML

Remove closing HEAD tag
Move height and colspacing parameters into a style statement
Update background in TD tag to correct syntax
Add ALT parameter and close IMG tag
Add CDATA section to SCRIPT tags
Add missing closing P tag
Merge pull request #514 from ExolonDX/branch_08

Tidy up "system_firmware_check.php" XHTML