rename "completed" to "status" in the DB and code

current, the open vs. closed stuff is stored in a db column called "completed" and those are what the variables in the code refer to. this is confusing and wrong, since signups don't have to apply to events at all, and you can signup for nodes that don't have any notion of starting/stopping, or being completed.

attached patch changes the schema, modifies the code to match, and provides a DB update to migrate people's data.