We had inconsistent indentation in many places. Now we're fixing them
and adding a linter to our CI so we don't accidentally introduce
inconsistent indentations again.
Using the standard `confirm` parameter, we can remove all the custom
code we added to do the same thing.
Since the code is similar, we're doing the same when asking for
confirmation to send notifications.
In the same fashion Newsletters is managed, with the only difference that
the preview is using the notification partial in the same way the index
of notifications.
