Exit strategies refinement

[sthewissen]

Currently there are a few ways of exiting trades:

• Stop loss is hit - This is currently implemented in a way that the bot checks whether or not the stop loss was hit. Ideally this is done by placing a stop loss order which is way more accurate. However, Bittrex does not support this...
• Trailing stop is hit - See previous.
• ROI is hit due to trade time constraint

What is currently not implemented:

• An exit strategy telling you to sell

I'm still looking for a way to refine this. I can imagine someone wants to use these features depending on the strategy they use? Perhaps these should be enabled through that? If the Prepare method returns a sell action we can use that in the ShouldSell method and the options above can be enabled/disabled in the strategy itself?

[sthewissen]

Created a functionality that checks the current strategy for a TradeAdvice.Sell signal to sell things. This is currently active on develop.