complete user new.html page, including a sign up link so that a user can be signed up.
rename all sessions to appointment so that a user session will be created.  I think Session class is reserved for users?
create new & create actions for sessions controller; create new.html for sessions class so that user has a page to log in from; add login link to layout.
create private method in ApplicationController to help with finder a currently  signed in user; implement if statement in application.html for a currently signed-in user to show that they are signed in; add some css customizations.
create destroy action for SESSIONS controller and add a logout link to application.html so that a user can logout.
create better routes for users#new, sessions#new, and sessions#destroy; match better routes to links in  application.html.
create basic authorization for creating a new user so that only loggedin users create new users; create link on application.html for currently loggedin users to sign up a new user.