Bug 1006569 - [privacy] Add checkbox at sign-up

Functionally works fine for me and all the tests pass too.
I will add the unit tests and modify helper text later today and need to discuss about the deletion of user email from database usecase.

Sorry, I should have caught this before, but we shouldn't be including the locale in this label. It should just read `https://oneanddone.mozilla.org/profile/`