Renamed AnswerSheet to simply Worksheet
[Decoupling #1]: Storing quiz layout information in a new model - Draft

The layout of a quiz impacts many operations - from what QR code is
set to how scans are received to how report cards are generated

Unfortunately, the current system assumes only one invariant layout per quiz,
the details of which are scattered across models. Any computation
requiring layout information is therefore pieced back together afresh everytime.

This decoupling will also help us assign a page-agnostic QR code
to every response in the future
Dropping the idea of maintaining multiple drafts for Quizzes ...

There are other re-wirings that are more essential. For now, we can
live with the fact that a Quiz can have only one layout. Any teething
problems due to recent change in layout algo. can be handled on a  case
by case basis
Renamed Testpaper -> Exam

An Exam is nothing more than a collection of worksheets. Its only
created if the teacher does NOT publish a quiz. Otherwise, only individual
worksheets are created for students
Some more references to testpapers replaced with those to exams
 AnswerSheet -> Worksheet
Simplied code for calculating Exam.mean?

It should always been as simple as it is now. We were in fact under-reporting
the class average in our mails
Merge branch 'master' of https://github.com/abhinavc/web-application