Refactored BTCE

Hmm. I'm rather new to both github and java, but since I used the Xchange library in some of my programs, I'd like to contribute back. Sending pull request now. 

Please do check through the changes I've made. I'm not too sure if it's what you're looking for. It's my very first project both in github and maven, so please be nice :)

Oh, and I also added a bit of code to the BTCBaseService, to try to work around the nonce errors that a few people have been mentioning - I added a 50ms delay between the retrieval of every nonce, which hopefully will be enough delay that the server will receive the requests in order.

BTC Address (if i actually did the refactoring correctly): 16HQ6vU58THxHvLS7Qx9Es8uvTWAtwHyGr