Implement the optional 'Record Activity' for sent reminders

The "Scheduled Reminders" feature includes an optional 'Record activity for automated email.' checkbox (record_activity in the schedule table). The send reminders cron job needs to check that column value and if true, insert an activity record for each reminder sent.

1 Create a new reserved activity type = "Reminder Sent"
(modify upgrade sql to insert this option value row)

2. Inserted "Reminder Sent" activity properties:
Subject : Use title from the scheduled reminder record
Details : Contents of the scheduled reminder (message body)
Target Contact: The reminder recipient
Source Contact: Same as source contact of the activity triggering the reminder
Date / Time : now()
Status : Completed
Source Record ID : activity.id of the activity triggering this reminder