Closes #1

Closes https://github.com/erocci/erocci/issues/52

Backend API: send only entity id to backends, not full entity, not to confuse what's actual version and modified one

Closes: https://github.com/erocci/erocci/issues/59

WHen creating an entity updating a collection, use id for generating collection if anym else generates id

Use backend's optional callback: mnesia_disc_copies/1

Fix error renderin