(parrtially) completed MenuManager;
added:
(1) bool isDataModified; // checks if data had been modified
after open
(2) save option
(3) save as option
(4) quit option

TODO:
(1) write data to file (breadth-first traversal)

FIXME (High Priority)
(1) invalid output for Url
(2) bad_access problem

FIXME (Low Priority)
(1) memory leaks of unexpectedly exit // through exit();