Adds missing User Group / User icons on ACLs page

**BEFORE:**

![access_control_lists_-_before](https://cloud.githubusercontent.com/assets/352182/2931625/cdfbf0ce-d7a5-11e3-9e0d-53f4136725c1.jpg)


**AFTER:**

![access_control_lists](https://cloud.githubusercontent.com/assets/352182/2931617/afa4c786-d7a5-11e3-82b4-6164af3a0948.jpg)