Update 404.php

Since in index.php we are chekcking is_404() then class should be "rtp-singular" in section tag. So in 404.php in section tag there should be same class applied.
Corrected footerbar-widget class selector
Merge pull request #57 from singhsumit/master

Corrected footerbar-widget class selector
Merge pull request #50 from ankitrox/patch-1

Update 404.php
Merge with rtPanel 4.0