Solve csrf problem on mobile.
Add cards play page and new_words play page.
Add routes and write logic for api /new_words/delete /cards/add /cards/schedule /cards/delete
Finish play new word page.
Fix the bug that user.study_new_word_cout and user.study_card_count don't increase properly.
Fix bug that temp files generated by open-url were not deleted sometimes.
Add client side Word and Card model.