Automatically collect relevant citations to encourage external contributions

[tkuchida]

As part of our effort to encourage external contributions, I propose automatically generating a text file (e.g., "authors.txt", "contributors.txt", "references.txt") that lists the publications associated with the model and algorithms that were used to generate results. Initially, could simply call Object::getReferences() on all objects when exiting from Tools and report a list of (unique) strings.