Use simple id for entities

This is rebased against latest master:


"Currently, custom name for identifiers were set (user_id…). I suggest don't change the default because it brings zero advantage, but rather a very annoying disadvantage.

When doing associations (especially with something as common as User), Doctrine assumes that the identifier has the key "id". If it's not the case (as it is currently), you need to manually set a JoinColumn so that the association is correct. This is very annoying, and can be forgotten easily.

So I suggest having the easy way and leave the default here."