Maven plugins specific versions set.

Maven uses some plugins for basic operations within the build lifecycle
such as the compiler / clean plugins, if no explicit version is set per plugin
maven downloads the latest version it is aware of (statically defined within the maven package)
and may cause missing plugins when working in offline mode.

This commit contains an explicit set of the maven plugins versions.
Vertex native identifier with index support.

- As most graphs support indexes, the versioned graph currently requires
the base graph implementation to support indexes (implements IndesableGraph).
- A versioned vertex is naturally identified by a unique property and is
automatically indexed.
- Removed vertices are removed from the natural identifier index.
- Only active vertices are indexed, historical vertices are not indexed at all.
- Tests for natural identifier index.
- New base test, required for supplying graph configuration when graph instance
is instantiated.

In order to enable natural identifier the VertexGraph configuration
must enable the autoIndexVertexIdProperty property.