This commit fleshes out the `BatchEmailNotificationJob` and adds a
preview for the email that will be sent.

This commit adds the new job to the queue whenever a new tenant is
created.  Also adding a method to the `User` model to mark all
undelivered emails as delivered when their batch email frequency is
changed to 'off'.

The prior default value of `off` appears to be a reserved term
and did not work for i18n translations.

- Show email frequency on user profile
- Add selection list to edit profile menu to update frequency
- Add appropriate translations to en.yml

Ref: scientist-softserv/palni-palci#1022

This commit will ensure the correct bootstrap class is on the batch
email frequency select box.  It will also use the font awesome calendar
icon for the label.

Since it seems 'off' was protected, we switched to 'never' instead, this
commit will clean up any other places where it was set to 'off'.

This commit will add a callback for `Mailboxer::Receipt` to mark the
receipt as delivered if the user set their batch_email_frequency to
'never'.

This commit will add a few specs and also redo the logic for the batch
email notification send frequency.  We needed a migration to the users
model to track when the last email was sent to check if it's time to
send another one based on their batch_email_frequency setting.

This commit runs the Google translations for i18n files.

This commit will add the Site's application name into the email subject
as well as the body.