Add fields to User model

* Privacy flags (fixes #58)
* `is_minor` (fixes #56)
* Opt-in flags (needed for profile page)
Make `apps/users/views' a package

View files grow and grow. For now separate into `user.py` and `group.py`.
User profile page basics
Ignore migrations when running `flake8`
Merge pull request #94 from RickMohr/user-profile-basics

User profile basics