Add qaptcha to oj

1. add submodule QapTcha in static/
   according to http://www.myjqueryplugins.com/jquery-plugin/qaptcha
   github https://github.com/alpixel/QapTcha
   and fix a few things to make it look good
2. write /oj/qaptcha/key method in views.php to replace QapTcha's php/Qaptcha.jquery.php
3. add check_qaptcha() in views.php to check qaptcha validity
4. add qaptcha.html to include init scripts