Entity status + drafty

Same changes as https://www.drupal.org/node/2389185
Nothing ever gets stored in {cps_entity} with a changeset_id of 'published'.

There is the 'initial' special changeset too, but that's not changed here.

The published changeset is in {cps_changeset} but I wonder whether that should actually be in the table at all - it's really a "magic" changeset that things can't be assigned to.