Remove the _is_navigation special check in chaining

[MarcCote]

With the new and better chaining that supports nonlinear quests, there might not be a use for the special check self._is_navigation(nav_parent.action) when checking for action dependencies. That check was originally added to help generate more interesting (read longer chains) "linear" quest. Once PR #17 is merged, that type of quest could be still generated by decomposing it in multiple subquests.

For instance, take key > go north > unlock chest with key would be decomposed into the following subquests: (take key, go north, unlock chest with key) or maybe (take key, go north > unlock chest with key).

[kumaran-14]

Can i do this?

[MarcCote]

Hi. Fixing this issue requires a good understanding of the forward/backward chaining algorithms. If you feel comfortable with those please give it a try. Make sure your PR has proper unit tests showing that the same kind of quests (i.e. long chain of actions extending to multiple rooms) can still be generated, though (i.e. probably with a quest breadth > 1).