Lots of changes - many files changed
Now compiles - fixed some types and added some imports
Fixed tags (Bookstore, Registration, etc) - now extends Activity instead of implements
Cost, Effort, and Time classes are now finished (and are now immutable)
Added Checklist and ChecklistBuilder classes
   Checklist has methods for setting the bookstore, dorm, etc
   ChecklistBuilder takes a complete checklist and calculates the total cost, time, and effort