Algorithm for finding groups of persons who know each other.

Note that this algorithm is not done 100% nicely as there is no need of few methods (creating groups). For simplified version check here: https://github.com/JanuszHain/Android_Playground/blob/master/app/src/main/java/pl/janusz/hain/androidplayground/usecases/group/SearchForGroupsOfMutualPeople.java