Move entity storage related hooks to pre/Post methods on entity classes

Updated: Comment #N

Problem/Motivation

The more storage-agnostic logic we have in storage classes, the more work it is to provide an alternative implementation we need to rely more on base classes.

Proposed resolution

As agreed in in #2095283: Remove non-storage logic from the storage controllers, we want to move most (all?) hook invocations to the entity classes, as part of the pre/post methods, so that storage controllers only have to invoke those.

Remaining tasks

Most are easy, but we need to figure out what to do with a few special hooks, afaik right now one revision related one, which probably should get a corresponding method on the entity class and the translation hooks.

User interface changes

-

API changes

Shouldn't affect code outside of storage controllers as long as entity classes invoke the parent implementation of their pre/post method overrides.