Move create{Node,Relationship} over to the Kernel API.

As of this change all mutating operations have moved over to the
Kernel API, getRelationships(*) still remain in the NodeImpl.
These are not as "dangerous" to be able to mix with Schema operations
so they can wait another short while.
Merge pull request #1133 from thobe/2.0-schema-and-data-tx-for-create-node-and-relationship

Move create{Node,Relationship} over to the Kernel API.