Fixed many bugs. Solved all of the problems we were having earlier
today. Refactored and simplified code. SessionDetailActivity always
reflects the current checked in/out state. A new static SessionList
class holds all information about the sessions, keeping updates
synchronized between activities. GeofenceTransitionService monitors
geofences for all upcoming sessions (not just the top session) so that
the app will continue to work all day even if the user doesn't tap
refresh. Users *should* be automatically checked out when they leave
session the or when the session ends.