Added settings for show_upcoming_events and show_past_events to control ...

...whether or not lists for these show on the main page. Added a setting for calendar_position to control the position of the calendar relative to the lists, as above them, between them, or below them. These new settings are held in a calendar_settings object, as they pertain to the full page, and not to the upcoming_events_settings (renamed to be more explicit) used for the upcoming_events_widget.