added user authentication - pending authorization

user authentication completed 
1. user can sign up
2. user can sign in
3. user can logout
4. if user does not complete all the required fields on the sign in form, he/she will not be able to create their profile, sees an error message
5. if user enters the incorrect username/password when logging in, he/she will not be able to log in, sees an error message

Pending work on user authorization - to differentiate between admin and client(regular user)

Also added gem annotate to Gemfile, running annotate in command line adds schema information at the very beginning of corresponding models