[gh-498] Remove #maincontent width:960px css from unl_wdn theme

We previously had the broken templates that had a placeholder body class. The fixed templates now add class of "fixed" to body.

There is old css from before the templates were responsive that forces maincontent 960 wide so the edit tabs would always appear in the same place in the upper right even if the content was not 960 wide.

Now that the templates are responsive we can't have that.