send email when quota is reached

Closes #23 (closed)

1. I had two email templates sketched out: near quota, met quota. For now, we don't have a way of detecting near quota, so it's not happening. Deleted that, moved "met quota" into the right directory, and updated the contents to work with the context vars we want to use.
2. Updated tasks.py to send an email while flipping the is_accepting_events boolean to False
3. Updated a throttling test to look for the presence of an email. Had to add a user to the org in order to make the test pass.
4. Made the new email.py file to build and send the email.