Description:

Stubs out a new notifier and its views. Passes the notifier name, either
CamelCased or under_scored, and an optional list of push notifications
as arguments.

This generates a notifier class in app/notifiers.

Example:

rails generate pushing:notifier TweetNotifier new_mention_in_tweet

creates a TweetNotifier class and views:
    Mailer:     app/notifiers/tweet_notifier.rb
    Views:      app/views/tweet_notifier/new_mention_in_tweet.json+apn.jbuilder
                app/views/tweet_notifier/new_mention_in_tweet.json+fcm.jbuilder