Models modified.

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.
Changes made as per the suggestions.
TestCases Separated
Added assertion in test_get_random_questions, to check the order of questions.
Made changes to update_total_marks method
Merge pull request #25 from prathamesh920/question_paper_generator

Question paper generator
modification in models

Added shuffle option in the question paper.
Added language field, passing criteria and prerequisite quiz in quiz.
Added pass/fail result and percentage field in the answerpaper.
Added test for new model fields and new methods created in models.
Changes made to quiz form to accept prerequisite quiz.
Changes in edit quiz view to set prerequisite
changes as per suggestion
Made pass field as boolean field.

And changed variables to lowercases
Made the minor change
Mutiple correct choices question type added.
Merge branch 'model_modification' into multiple_correct_type
Merge pull request #26 from prathamesh920/model_modification

Model modification
Merge pull request #28 from prathamesh920/multiple_correct_type

Multiple correct type
changing moderator's landing page to show list of all quizzes
changes for user dashboard
adding marks obtained & percentage