clients that workout based on a plan

At this milestone I have clients that accept a workout plan, and will take and put weights from a rack based on the plan. There are two types of clients: AverageJoeClient, who puts weights back in the right place if possible, and RandomClient, who puts weights back in random slots, regardless if the correct spot on the rack is available. The demo at this point shows it only takes one RandomClient to screw it up for everyone else!