Implemented email body generation part.

And changed the interface of "send_items_by_email" function. Now it
receives u_item_array because it needs wordbook_url to generate
message body.
Done some refactoring works.

- Moved smtp_settings from source code to config file.
- Moved the initialization of ActionMailer::Base to reminder.rb.
- Changed the pick_items_from_db function to private.