Put back cog icon for multi-select batch actions

The cog icon was removed in f4b080e for whatever reason (doesn't seem clear, the commit is quite large), this pull request puts the icon back.

Any reason why this was removed? I noticed this because the batch actions dropdown had extra left padding which looked like where an icon should've been, but it was missing. This icon appears in 3.0.x, however.

There are a few unrelated SCSS compilation changes, probably because I'm using the latest version of Compass, version 0.12.2.

Attached screenshot below of the icon back in it's place :)

![cog_icon](https://f.cloud.github.com/assets/138450/506020/c8c48a8e-bd3f-11e2-8363-1a9a47ec5404.jpg)