Renaming methods in Graph.cs

Methods:
AddVerticesFrom -> AddVertices
AddEdgesFrom -> AddEdges
Adding missing Clear method for Graph.cs

Methods:
Clear: Remove all vertices and edges from graph
Modifying edge insertion in graph.

Adding edge reverse for Edge class:
(T1, T2).Reverse() -> (T2, T1)
However, (T1, T2) == (T1, T2).Reverse()
Merge branch 'graph' into dev