Modify/rethink Entity init functions

[Stephan-S]

We have to rewrite/rethink parts of the Entity.init() functions.
With MongoDB we do not yet have a valid ID for the element before we save() the element once.

This is a problem since many attributes call modify functions during the init() function which already require a valid ID / DB entry for various functions like accessing the corresponding path which is bound to the ID.

We either have to re-add the VMID attribute and make the paths and so on dependable on this ID instead of the DB entry ID or check if it is possible to create a dummy element with MongoDB to get an ID right from the start.