Remove passage and get broken links with streams

Is your feature related to a problem? Please describe.

Need better validation for links and customizability for the passages map.

Describe the solution you'd like.

Implement two new methods for the Story class.

1. removePassage: Removes a passage from the passages map. A passage can not be removed if it has other links connected to it.
2. getBrokenLinks: Retrieves a list of Links which points to a passage which is not in the passages map. Checks links that each passage in the passages map has.

These methods have to use java streams.