Added missing return statements to remove method
added missing return value to overwritten addParents
duplicate removal of partnership from node map
Fixed bug in isRelatedTo and changed parameter type. Modified remove to support the change

isRelatedTo now takes in two parameters:
- nodeID (the id of the node we're checking for relationship with)

- visitedNodes (a list of IDs of visited nodes)
fixed bug where actionstack pointer advances past the stack size
renamed variable and refactored undo method