Korean translation

Thanks to #2599, I could add new :kr: Korean translation!  Although there are some missing translations, the most of messages are translated to Korean.

![Home](http://i.imgur.com/6ygCHcE.png)
![Profile](http://i.imgur.com/t1UBzXc.png)
![Credit card](http://i.imgur.com/yKMXrJX.png)
![Widgets](http://i.imgur.com/kiWNRcC.png)
I left these untranslated messages in English, because I could not find their exact context.  This Esperanto message, however, is unintentionally left in Esperanto.  I will fix it.