Template the emails

Yup. They're templated now. I wasn't sure how to grab the current commit version for the email footer without cluttering up the config too badly (using `subprocess` would make it really ugly). Emails also send in HTML now, although I copied the `TODO` somewhere else because it should be text + HTML multipart emails.

Do you still want the `/email/to` endpoint? Seems kinda obsolete these days.

Fix #24 

#### Migration

I think you'll just have to copy `serverconfig.py.example` and update the settings again. I updated it to use `Flask.config` to give templates access to the config settings and then added settings for `DOMAIN` (for you, probably `http://leiyu5.cs.binghamton.edu`) and `COURSE_NAME` (for you, `CS 140`).

As usual, I'd double check to make sure that emails are sending appropriately with correct links, information, etc.