BitfinexBrokerageModel Doesn't Define Supported Order Types

[AlexCatarino]

Expected Behavior

BitfinexBrokerageModel doesn't allow placing orders for unsupported order types.

Actual Behavior

BitfinexBrokerageModel allows placing StopLimit orders, resulting in

System.NotSupportedException: BitfinexBrokerage.ConvertOrderType: Unsupported order type: StopLimit

Potential Solution

Check for supported order types. We support market orders, limit orders, and stop market orders.

Reproducing the Problem

Place stop limit order with a BitfinexBrokerageModel.Bitfinex.

Checklist

• I have completely filled out this template
• I have confirmed that this issue exists on the current master branch
• I have confirmed that this is not a duplicate issue by searching issues
• I have provided detailed steps to reproduce the issue