Enhancement - WhatIsIt item name support

Just a minor change to the getDisplayName method to include WhatIsIt support.

[WhatIsIt](http://dev.bukkit.org/bukkit-plugins/whatisit/) is a plugin which acts as an item database that users can add items to if they please. This is useful for Tekkit/Cauldron servers, as users can give friendly names to items added by Forge. For example, users can assign a friendly name to a Digital Miner from Mekanism, and its name will display exactly as they assigned it, instead of displaying MEKANISM_MACHINEBLOCK.

I've been testing the changes over the last couple of days on my server, and it looks to work flawlessly with and without WhatIsIt installed alongside it :)

Here's an example of it in action:

Without WhatIsIt
![Without WhatIsIt](http://i.imgur.com/LxDpad8.png)

With WhatIsIt
![With WhatIsIt](http://i.imgur.com/YoTHYA8.png)

Default name for items that don't exist in WhatIsIt is 'Unknown'.