Add "error handling" to Japanese edition

Add a translation of "error handling" in Japanese edition, and revise the whole translation.

FYI: [Dwango](http://info.dwango.co.jp/), the largest video-sharing company in Japan, said that their [live video streaming website](http://live.nicovideo.jp/) has been moved from PHP to Scala, and adopt the *Effective Scala* as their coding conventions :) ([Slide](http://www.slideshare.net/sifue/developers-summit-2014-play2scalaweb/57))