itty.next() is invoked twice in VersionedVertexIterable:iterator:next()
Public visibility for getting last graph version.

This commit also contains a bug fix when initializing the configuration vertex,
as in transactional graph a commit should occur immediately after the vertex creation.

Also the identifier of the conf vertex should be GRAPH_CONF_VERTEX_ID constant instead of
a textual representation of "GRAPH_CONF_VERTEX_ID,".
Multiple bug fixes in transactional versioned graph:

- Added graph a constructor to support 'configuration' param.
- Mistake in the log of the 'added edge' phrase (wrote 'removed' instead of 'added')
- Bug fix when initializing the map which contains the modified old properties of a vertex.
- Ignore the invocation of modified vertex properties events in case the vertex is just created in the current transaction to avoid the creation of historical vertices.
Javadocs insertions