modified send_notifications_for_cert routine to decrease
 db load

Rather than making a query for each device, we can get all unsent
notifications for a given app with one SQL query.

The change also required a slight update of the app_spec.

from https://github.com/PRX/apn_on_rails/pull/25
RAILS_ENV is now deprecated

from https://github.com/PRX/apn_on_rails/pull/43
Only update noty.sent_at on successful write

from: https://github.com/PRX/apn_on_rails/pull/55
incompatible character encodings: ASCII-8BIT and UTF-8

from: https://github.com/PRX/apn_on_rails/pull/61