Possible feature of extending a config from a separate class

[jwoertink]

Mentioned by @matthewmcgarvey https://github.com/luckyframework/habitat/pull/59#pullrequestreview-605695502

Right now just toying around with the idea that maybe we allow you to create a class with options, and use that to extend an existing one.. Sort of merge settings... Not sure how all that would work exactly, but I wanted to open an issue just to track it