Filtering internal edges

Generally when returning an iterable of versioned edges, the internal edges
are not interesting and should be filtered, except special cases such
returning a historical vertex chain or when handling edges internally.

This commit:
- Introduces the possibility to filters/include internal edges.
- A method to identify an internal edge.
Introducing a VersionedContextGraph.

Version context graph is a graph wrapper which performs graph operations
for a certain version bound during context creation.

This make it possible to perform queries such as:
//Get all vertices for graph version 1
vc(1).getVertices();
//Get the value of property "key" for vertex id 4 for graph version 1
vc(1).getVertex(4).getProperty("key")

Fixes #2