Create User model with password/confirmation

Generate a user model. Write specs to verify that the User: has a password, has
a password_confirmation, and they match
Implement sign up feature

A user can now click a sign up button and sign up for an account. The user is then
redirected to accounts#index
Implement profile page

A user can now visit their profile page and view their username and email.
One can also edit thier user attributes