Remove "example.com" in Signup Confirmation Email

[banesullivan]

The signup email lists example.com all over the place. We need to fix this: (I removed my email and the signup link which were correct)

Hello from example.com!

You're receiving this e-mail because user ..... has given your e-mail address to register an account on example.com.

To confirm this is correct, go to ........

Thank you for using example.com!
example.com

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It seems that site_name in https://github.com/girder/django-girder-style/blob/master/girder_style/templates/account/email/base_message.txt is incorrect

[banesullivan]

This was fixed by renaming the default site entry in the admin interface for each deployment.

[banesullivan]

We need to recover this migration from the cookie-cutter which was deleted at some point: https://github.com/girder/cookiecutter-girder-4/blob/master/%7B%7B%20cookiecutter.project_slug%20%7D%7D/%7B%7B%20cookiecutter.pkg_name%20%7D%7D/%7B%7B%20cookiecutter.first_app_name%20%7D%7D/migrations/0001_default_site.py