Feature/insert node into tree

[electronicbites]

Implements a tree aware insert_node and delete_node Also a a fetch tree function based in CTE which are adding a virtual attribute level.

I split the changeset of Node into different usecases.

I needed to rebase which produced a tons of conflicts. So there might be some errors left. For instance the broadcast function in create_node and update_node_content should be removed again I believe. I cannot remember that I was adding it ;)

Questions arise:

Should all the tree aware functions to a new module? do we still need a simple delete node or create node? At least ones that are public?