Added Registration, Login, and Logout pages

- Added option to register, login, and log out with functionality.
- User can click log in button, and on log in page, can choose to create
an account if they don't already have one.
- User is directed to registration page where the must enter username,
password (twice for validation) and email - if any field is blank or
passwords don't match, registration is not completed and user is
notified via alert box.
- Successful registration redirects user to login page.
- User enters login creds; if they don't match any records in DB, error
message is shown, otherwise user logs in, session is created, and user
is redirected to their profile page where they can modify or update
profile (username, password, email) information (functionality not yet
implemented).