SimpleDirectedGraph: added VerticesIterator, implemented iterator
TestSimpleDirectedGraph: implemented testIterator
deleted: SimpleGraph, UnmodifiableList
Graph: changed arguments for connect and get from int to T
SimpleDirectedGraph: fixed
TestSimpleDirectedGraph: fixed
SimpleDirectedGraph: changed contains and remove to work with Id type,
fixed connectAndGet, getNewEdge, connect, ConnectionsIterator.add
TestSimpleDirectedGraph: fixed