Refactored TheRemoveVertexMethod tests in GraphUnitTests
Refactored all methods tests in ArcUnitTests
Refactored TheConstructor tests in TwinVertexTests
Refactored adding edge to TwinVertex to AddEdge method

Merged AddNonMatchingEdge and AddMatchingEdge into AddEdge with bool
parameter
TwinVertex.AddEdge returns Tuple<Arc,Arc>
Refactored TheNameProperty tests in TwinVertexTests

Moved TwinsHaveNameOfPrecursorWithTypeAppended to ABVertexTests