created last_channel method so we can access the last channel associated with a given project without digging deeper in the model
now we render a text template to build the notification subject, we need this to get rid of the old mail_params since we cannot use ruby code inside translations
added channel to notification as projects can belong to multiple channels we want to know which notification was sent to each channel
added method to always retrieve the same update number for a given update
fixed credits_warning notification
added subjects for all notifications as text templates
fixed specs
fixed channel notifications when we do not have a channel for the project
fixed new_draft_recipient