With this commit we are logging which emails have already received the
newsletter
This could be important if something goes wrong sending the newsletter,
to be able to identify which users have already received the newsletter
and be able to skip them
We’ve had to add a new action to the Activity model (email) and add
paranoia features to be able to deal gracefully with the default
`with_hidden` scope in Activities[1]
[1]
https://github.com/AyuntamientoMadrid/consul/blob/master/app/models/acti
vity.rb#L2
