Add equalsVertex/equalsEdge methods to VertexFrame/EdgeFrame interfaces.

This allows testing for equality based on the underlying element type,
regardless of the Frame interface used. Note that the current behaviour
of the equalsVertex/Edge method checks the equality of *either* another
Vertex/Edge object _or_ another VertexFrame/EdgeFrame.
Cleanup.

Remove unused imports and unnecessarily extended CreatedBy class.
Merge pull request #14 from mikesname/vertex_edge_equality_methods

Allow comparison of framed vertices based on their vertex, not framed class...