Fix Enrollment Email UI/UX

@jrbl @caesar2164 

Fixed enrollment email UI in Studio. The list of changes is as follows:
    - Test Email functionality: can now send yourself a test email from studio
    - Set default template button: can now click a button to replace email
        with the default template
    - UI changes: html ordering and structuring
                  Got rid of enable_default_email button. Pushed this feature
                  to the default template button

Things to note:
    - default template is stanford-specific.
    - minor test changes (since enable_default_email field is gone now)

![screen shot 2014-07-30 at 12 48 48 pm](https://cloud.githubusercontent.com/assets/3598201/3755213/a65ef2ce-1822-11e4-9b63-d01e16be444f.png)
![screen shot 2014-07-30 at 12 49 07 pm](https://cloud.githubusercontent.com/assets/3598201/3755214/a65f7c30-1822-11e4-8c06-cfdc32c476af.png)
![screen shot 2014-07-30 at 12 48 28 pm](https://cloud.githubusercontent.com/assets/3598201/3755215/a66022e8-1822-11e4-8005-c7200f417886.png)

Can we rename this? Since our Python test suites use the convention of naming test methods `def test_*():`, I was initially confused here and thought this was some sort of assertion. Since we're not actually "testing" something here, as opposed to "sending a test", maybe add a prefix, something like
- `def send_test_enrollment_email(request):`?