Ogm 521 natural one to one

https://hibernate.atlassian.net/browse/OGM-521

This patch will remove the redundant column created for *ToOne associations on nodes.
I add to add some metadata in the TupleContext to achieve this.
We shouldn't use an array as map key; gets will be doomed to fail as a contained keys and given look-up keys will not  be equal (despite having the same contents). A wrapper type should be used instead as key (which delegates to `Arrays#equals()`/`Arrays#hashCode()`).