Updated Quizes to store the SessionType that is indicated by the
AddAssignmentView radio buttons.  The Course view now only allows
users to pick a session type for lessons (not quizes).

#47
Closes #39
Merge branch 'master' of https://github.com/lingolearn/lingolearn.git
Updated the enumeratoin to pretty print the output.
Updates to the code and reworked SessionTypes so that getEnum returns
the correct object.
Corrected issues with the SessionTypes and added a unit test for them.
Reworked unit tests to get better code coverage.
hooked up spatial repetition algorithm
Merge branch 'master' of https://github.com/lingolearn/lingolearn.git
Instructor view of analytics table displays student name instead of id
Changed QuizPresenter to correctly retrieve confusers based on the
session Type.  Changed the CardService to accept SessionTypes 
parameters on confuser method.  

#47
Student analytics table displays numbers in percentages
added "All course" option to research view
Merge branch 'master' of https://github.com/lingolearn/lingolearn.git
added a "back to course" button in sessions
spaced repetition algorithm is now supported for courses
Changed QuizPresenter to correctly represent the card 'question' and 
'answer' options based on Session Type.

#47
Working on reviewing the code.
Merge branch 'master' of https://github.com/lingolearn/lingolearn.git
Merge branch 'master' into analysis-milestone-three