added "addShowing" method to ShowOption and TimeOption
added SelectableOption
refactored ShowingOption to inherit from SelectableOption
added automatic link between showing->show and showing->time
adding handlers for show option to talk to showing
added timeslot class and tests
added CalendarDate class
added TimeOfDay class and tests
renamed CalendarDate to PerformanceDay
renamed PerformanceDay to Day
renamed calendarDay references in TimeSlot to 'day'
fixed bugs with selection option sub-classes

fixed bug where timeslot and show were not defaulting selectable to true

fixed bug where timeslot and show were ignoring whether they were
selected when checking to see if associated showings could be selected
finished integration tests

completed integration tests

several bug fixes along hte way
added Venue class
added link back from venue to show when show added to venue