UC 41: Implemented Sending Reminders

This implements UC 41 Subflow 1: Send reminders to patients from admin account and UC 41 Subflow 2: View reminder outbox from admin account

You can test it with mvn install -Dtest=ApptDAOTest test, mvn install -Dtest=SendRemindersActionTest test , and mvn install -Dtest=SendRemindersTest test