remove traces of Swift because testing with it doesn't pay off
test Core Data Stack usage with Obj-C tests

- add PersistentStack
- use MOC in ShiftTemplateController instead of store URL
- add PersistentStack properties to main view controllers
test CalendarProvider message broadcasting

- use doubles for notification center, event store, and user defaults
- add convenience accessors to EventStore(Wrapper)
put test helpers into their own files
use UserCalendarProvider throughout the app instead of NSUserDefaults access

- add coarse test for CalendarAccessGuard
- rename EventStore to EventStoreWrapper
- rename CalendarProvider to UserCalendarProvider