Add private/extended api calls

[owenvoke]

Cryptopia has 2 API sets, it would be good to implement the private/extended API set as detailed here:
https://www.cryptopia.co.nz/Forum/Thread/256

This includes the following new calls, possibly under an Extended class:

• getBalance()
• getDepositAddress()
• getOpenOrders()
• getTradeHistory()
• getTransactions()
• submitTrade()
• cancelTrade()
• submitTip()
• submitWithdraw()
• submitTransfer()