Clean up imports.
Don't allow a detached edge to be detached a second time.
Prevent detachment of a DetachedMetaProperty.
Prevent detachment of a DetachedProperty.
Prevent detachment of a DetachedVertex.
Expanded tests to cover Property.key() to ensure hidden prefix is removed.
Stopped the PathTraverser from detaching already detached things.

Gets rid of some unecessary object creation - assuming it is unecessary.