adds letter opener configuration option to development env
adds authentication links to nav bar
adds filter on merchant, saq, scan controller to check for authenticated user, prompts user to sigh up if not
replaces 'edit profile' with the users email address when trying to link to edit user profile page
adds well and center align styling to login/register forms; adds margin between login forms and top nav bar
replaces 'sign up' with 'register', replaces 'sign in' with 'login'