Add a new status change event to the client timeline. This is the proper
way to change a client's status, as it maintains audit history.

Valid Status Transitions:

• prospect → processing, inactive, never-serviced
• processing → active, inactive, never-serviced
• active → onhold, inactive, hospitalized, hospitalized-er, in-facility
• onhold → active, inactive
• hospitalized / hospitalized-er → active, inactive, pending-discharge
• in-facility → active, inactive
• pending-discharge → active, inactive
• inactive → active (reactivation)