Put addNode, addEdge and getNodeEdges back into the base class, since the graph in the TextRank object will be declared as such.
Added TextRank class with tests for buildGraph method
Replaced Node<T> with T for addNode, addEdge, and in EdgeMap. This makes more sense as the node object itself is only required when its weight is to be fetched/modified.
Added toString method to Edge for ease of debug
Fixed buildGraph tests and added buildGraph code