Annoying type check problem when considering models of known type

[linusheck]

Suppose that your model is a POMDP, if you want to manipulate the actions, you still always have to fight against the typechecker because it thinks that actions might be None.

We've decided against using inheritance, so this is just a natural consequence of that.

One (complex) way to refactor the model class to fix this would be by using Mixins for all of the model features like actions, observations, etc, creating a seperate class for the model types.