Do not use *.exapmle files

This is just annoying. An extra step to instal the app that doesn't make
any sense.
Do not ingore environment files
Use ENV variables to configure rails app

Also, smtp settings don't have to be configured as long as delivery_method is set to :test, so just remove it.
Add .env and dotenv gem so people can easily manage credentials
STMP -> SMTP
.env内にMAIL_SENDERを追加
Localize用のymlを役割ごとにファイル分割するようにした。
・Articleに楽観的排他制御を導入。
typo修正