Workflow states should have a flow

[jace]

The Edit Event form allows the event owner to choose any workflow state. This should not be possible. All new events should be created in the Draft state and state change can only be via directed flows.

The required states:

1. Draft
2. Public
3. Closed

No other states are required. The possible transitions between these states:

1. Draft -> Public ("Make public")
2. Public -> Closed ("Close event")
3. Closed -> Public ("Reopen event")

When an event is in the Closed state, it is removed from all listings and no user activity is permitted. That is, users cannot create or join projects. They can still view projects and comment on them, however.