Use a partial to display all users
Add admin column to users
Test for presence and functioning of admins
Create an admin in db:populate
Add tests for delete options

These validate both DELETE requests and the presence of links. However,
an admin can still delete him/herself despite these test cases.
Add a FactoryGirl factory for admin users
Add a utility for signing in as a user without using capybara
Add delete button and destroy methods for Users
Fix typo (checked_sign_in becomes check_sign_in)
Add a Course model and associate it with User

The relationship between Courses and Users is that
Users can have_many courses by being in them, but they
can also have_many of them by teaching them. Similarly,
a Course can have_many Users by having many students
enrolled in them, but can only have one teacher at a time.
Therefore, the idea relationship model would be to say:

     Users habtm Courses (as Students -> Courses)
     Users have_many Courses (as Teachers -> Courses)

     Courses habtm Users (Courses -> Students)
     Courses have_one User (Courses -> Teacher)

This commit essentially does just that. Users will now
have access to the methods enrolled_courses and
taught_courses, which both return arrays, and Courses
will have access to teacher (returns a User) and
students (returns an array of Users).
Alias teacher and student to "user" in factories

These will probably be useful for tests involving courses.
Add a factory for creating courses
Add tests for assuring users can teach or enroll in classes
Add tests for course property validations
Have courses validate for the presence of teacher_id and name
Refactor tests for associations into one group and test for cascading deletions
Add dependent: :destroy for Users' taught_courses
Add font awesome
Test for signup too
Add sign up link to the header and remove it from the front page.