Added config param for default_email_locale

The default locale depends on the I18n.default_locale. This way we can
set a separate default_email_locale besides the I18n solution.
Fix for url_helper in #test_deliver action
Fixing weird turbolinks dependency error
Moving the explicit dependency on turbolinks into our app Gemfile
basic model for Preview mails
remove unused helpers
move formats and locales into model
i18n-tasks
fix email views
keyword args 2.0+
changes for v0.2.15
Bump to 0.2.15
refs #26 user Preview.mail_methods in generator
travis: add 2.1.0
Fix test_deliver
refactor
fix
changelog for v0.2.16
Bump to 0.2.16
acceptance test for email test send. fix param name