Adds holographic janitor signs

Port of https://github.com/NTStation/NTstation13/pull/400

![92a5bb06-ba16-11e3-94c4-02fd9280f60e](https://cloud.githubusercontent.com/assets/7247232/4566860/89c3e480-4f2c-11e4-9a58-4ca115f878cf.png)

Credit to goofball *and ausops!