Add support for extending the ktor server

[ningsuhen]

The embedded ktor server has some default routes. It would be nice if I can add a few custom routes to display other stats or data. exposing the server or a way to pass additional modules to the ktor embedded application will help.

[jbaron]

Can see how to make it easier to extend. Could make some classes and properties non final.

Out of curiosity, do you have particular use cases in mind of things you would like to add?

[ningsuhen]

Sure, there are few use cases I have now but they could be very personalized for my strategies.

1. I use the configuration as limits for the strategies and I want to display them in the UI.
2. I want to store some highs and lows across restarts in redis. So, I want to be able to view the values from redis via the web UI.