BUG Fixed broken ErrorPage icons in CMS view

The ErrorPage didn't have the right icon in the CMS, and was reverting to the basic page icon. This was due to a CSS error which I have fixed in this pull request.

It's not incredibly critical, I realise, but I didn't realise how obnoxious it was until I saw there was a problem in the SCSS.

I apologise for minor formatting changes in the resulting CSS file, which was the output of my version of compass (0.12.2).