Question paper generator

QuestionPaper model modified for generating random questions.
Added language field to Question model.
Removed tags from Quiz model.
Template and javascript for Add and Edit questions modified.
Added test cases for models.
This method is a little confusing as there is an attribute called `total_marks` already.  When you use this method, what is the intent of the code?  Think about that and please rename the method to something where this intention is clear.