User needs a way to delete their account

This resolves #272 

The assumptions made are:

1) Privately owned apps should be cascade deleted
2) Publicly owned apps should remain, but be unowned
3) All OAuth Tokens and Grants should be cascade deleted

- Updated some HTML on the Profile page
- Added a delete button on the Profile page
- Created a screen and action for entering the email and destroying the profile
- Added tests to cover UI and to check for models being deleted
- Changed the user model to cascade delete private apps and to nullify public apps
- Changed the user model to cascade delete OAuth authorizations