included autoplay for exams
exams/progress: page rendering according language: en-ru or ru-en
exams/progress: updated handler for correct answer for both en-ru and ru-en
exams/new: updated languages selector with choices prepopulated from back-end
exams: added 'completed' field to Exam model and put it as a filter for /exams page
Merge branch 'feature/exam-ru-en' into develop

* feature/exam-ru-en:
  exams: added 'completed' field to Exam model and put it as a filter for /exams page
  exams/new: updated languages selector with choices prepopulated from back-end
  exams/progress: updated handler for correct answer for both en-ru and ru-en
  exams/progress: page rendering according language: en-ru or ru-en
  included autoplay for exams