Fixes #8797 - Separate style from the HTML in emails

By using roadie-rails gem (1.1) style can be separated from email
html foramt, and absolute paths can be used.
style was separated to 'email.css'

Fixes #10649 - Adds Test email button to user's mail preferences

When clicked, a test mail deliverd to the user's email, and if it
failed, error details will pop up.

fixes #7586, #7734, #7172 - user preferences for receiving mail notifications

Adds a framework for user-selectable mail notifications. The work is
still done in ActionMailer classes and launch by rake in cron, however a
wrapper called MailNotification is used to provide RBAC and make the...