Why:
Both Newsletters and Email Downloads need the same logic: To extract the
emails from all the users in the segment that have newsletter flag
active, removing all empty email values.
How:
1- UserSegments#user_segment_emails holds that repeated logic and is used
on both Newsletter & EmailDownload.
2- Rename Newsletter#list_of_recipients to list_of_recipient_emails as
it is more descriptive. There is no need to pass entire Users around,
only the emails are needed at Mailer#newsletter method.
3- Cleanup Newsletter#list_of_recipient_emails model spec scenario
Why:
User with an empty email value (nil) should not appear in the recipient
list for a given UserSegment at Newsletters or Email Downloads.
How:
Using Enumerable#compact and Enumerable#select to filter out empty emails
Increasing Email Download feature spec and Newsletter model spec to cover
all possible scenarios including the nil email one.
Why:
UserSegments are not only used for Newsletters or Email downloads, but
also for internal Global Notifications. We don't want to have that scope
hardcoded inside UserSegments as users that have opted-out from the
newsletter should still be recipients of global notifications.
How:
Removing the scope from the UserSegments `all_users` method that acts as
base for all the other segments. Including that `newsletter` scope only
on the places that is relevant:
* When listing recipients for a newsletter
* When downloading a listing emails that can be newsletter recipients
Also updated relevant tests
