[Feature] Staff Chat similar to the one used in fCraft classic server software

Add essentials.staffchat to a group/user to allow them the ability to send a message to staff.
Add essentials.staffchat.read to a group/use to allow them the ability to see the messages being sent in staff chat.
Users that do not have permission to read staff chat will not see it at all.

![ScreenShot](http://i.imgur.com/fbNQjiy.png)