Add default root route

Point to UsersController#index for our default route so we go
somewhere.
Tests for admin user

We want to be able to support an administrative user and these tests
include that functionality in the model.  Other tests will be
necessary to fully test admin functionality.
Fix FactoryGirl test syntax

The previous test accidentally left out the create method call to
FactoryGirl.
Create an administrator User

We pass the tests that allow us to have an adminstrator user and
create one in the console while we're at it.
Test for User self-delete

We add a test that makes sure the user cannot delete themselves.
Test admin can delete others

We add a test to ensure the admin can successfully delete others.
Admin user passing tests

Now we pass tests with various modifications to other tests so that
the admin user does the right thing.

Conflicts:
	app/controllers/users_controller.rb
Refactor User before_actions to be simple

The before_actions were becoming complicated with multiple layers of
nested conditionals.  This simply cleans them up to do one thing and
only that one thing well.

Conflicts:
	app/controllers/users_controller.rb
Final tests for User redirection

This is the final set of tests that check that the user is properly
redirected when they try to perform an action that they shouldn't be
authorized to do.  The two examples in this commit are trying to
create a user while being logged in and the admin user deleting
themself.