Working on automated emails

#47, #21, #2
Reminder email changes

The reminder email is sent out 24 hours ahead of time instead of the day
of
Thank you email changes

The thank you email is sent 12 hours after a service
Fix issue with wrong route definition
Minor tweaks to some emails
Update to the message commands
Fix issues with the attendees modal

Fixes #53
Let students email the instructor
Update appointment creation

Provide a checkbox so that staff can choose not to send a notification
to the student
Add a method to check if a service has started