Use views relationships to go from node to schedule item, add is scheduled filter.

Issue Summary

I realized that for things to work sanely I need to require relationships from the {node} table to the {station_schedule_items} table. This means that if you want to see all the schedule items for a schedule you can do that or if you want to see all the times a program is scheduled you can do that. The only downside is that now you *have to* add a relationship to the view to get access to the schedule items.

I also added filters for schedule has programs and program is scheduled. I re-added the default views for scheduled/unscheduled as well.