Mime Backpack

This is just a small commit specifically aimed towards the mime. 

This adds sprites for a mime backpack(both for the mob and the storage), and the small bit of code for this new backpack and for the mime to spawn with it.

I have tested this on a local server and everything seems to work fine.

![mimepack storage](https://cloud.githubusercontent.com/assets/4686269/2569473/24b74918-b8ed-11e3-9192-0c3ea0e1ff4b.png)

![1 1](https://cloud.githubusercontent.com/assets/4686269/2571413/d1b4f9fe-b905-11e3-9af3-33e708052c82.png)



Say hello to Parcel Parceaux, the backpack which is to creepy to get stolen