Be able to 'switch' asset and currency

[timstoop]

System information

• Have I written custom code (as opposed to using zenbot vanilla): No
• OS Platform and Distribution (e.g., Linux Ubuntu 16.04): Linux Mint 18.3
• Zenbot version: Master branch
• NodeJS version: 8.9.3
• Python version: 2.7.9 (is Python used??)
• Exact command to reproduce: Any trade

Describe the problem

I'd love to see a feature where you can switch the focus of the bot. For instance, when trading poloniex.ETH-BTC, I'd like to be able to focus on increasing the amount of ETH instead of increasing the amount of BTC. I see no easy way to do this.