refactoring experiment instances
fix up tests and make them more robust
more refactoring of lobby, batches, and assignments
finish refactoring and initial test fixes
add more tests for refactored code
fix tests, hopefully for real this time
Merge remote-tracking branch 'origin/ensure-treatment'
tweak and make use of ensure treatment code
update database and display for new schema
Merge remote-tracking branch 'origin/exit-survey-display'
Improve display of completed assignments
correct git links in docs; fixes #10
move assignment and batch objects into private classes
Partially changed assigner to user assignment instead of user Id.
Fix lobby assignment tests
add payments on assignments
changed how IP address is saved on login, and add tests
fix IP address test
convert assignment instances to objects
Add tests for joining and leaving instances; update stored timestamps