added a post view so that a user can click on a post in the list view and view a page specific to that post.
added a navigation section; moved adding post to form in nav section; added filter to display host info from a url.
register.html   : created registration form/view
AuthService     : wrap angular auth service
AuthCtrl        : to allow user registration
app.js          : created route to view registration page.
nav.html        : shows if user is signed in and link to log out
NavCtrl         : injected AUthService so we can add logout function
allow user to log in with email/password.
added error handling: invalid account registration, login, etc.