Optional Collection Type for multi-occupancy

[ncollier]

Currently we use a std::list which may not be optimal for a larger number of agents.

• Test multi-occupancy code with std::list vs std::set and varying number of agents and see if there is any difference
• If there is a difference, provide user with option -- additional argument, update occupancy type argument, environment variable

[ncollier]

See this: https://baptiste-wicht.com/posts/2012/12/cpp-benchmark-vector-list-deque.html

vector might be better for our purposes -- speed of finding the element vs. replacing and resizing.