Create cron job to send "triggered emails" on an hourly basis

Implement a cron job that is driven by the schema as specified in: CRM-8150

I would split this into the following tasks:

• Design the database tables you need to keep track of what has been done so far
• Implement the cron job and ignore repetition but keep track that the email was sent and when
• Incorporate repetition into the cron job process
• For now the unit of time is restricted to days and hours only
• Add hooks at various stages of this workflow, so the process can be overriden / enhanced etc

Would be good to think about these issues also:

• Can we make it an option to use CiviMail vs sending email one at a time
• Can we make it generic enough to handle the "non-activity" related use cases of the schema