Abstract CTENode should be split into base class without parent link

[eskhool]

If the CTEnode _cte_node_parent link has to be usable to allow for a different FK to 'self' then the rest of the clean and other functions should be in a CTENodeBase Class and only the link called parent should be in the CTENode class.

Presently all the help functions in CTENode also do not seem to hard coded to _cte_node_parent?